Valve Selection For An Engine Operating In A Multi-Stroke Cylinder Mode

ABSTRACT

A method to control valve patterns in a cylinder operating in a multi-stroke cylinder mode. Valves are controlled to improve drivability and emissions.

The present application is a continuation of U.S. patent applicationSer. No. 10/805,625, filed Mar. 19, 2004, entitled “Valve Selection foran Engine Operating in a Multi-Stroke Cylinder Mode”, the entirecontents of which is incorporated herein by reference.

FIELD

The present description relates to a method for selecting valves tooperate for a cylinder of an internal combustion engine and moreparticularly to a method for controlling valves that may be deactivatedto improve vehicle drivability and emissions.

BACKGROUND

Multi-stroke engine operation (e.g., varying the number of strokes in acombustion cycle) is one method that may improve fuel economy whilemaintaining reserve torque capacity for elevated load conditions. DuringMulti-stroke operation, selected strokes of each cylinder may not followa typical four-stroke cycle for some conditions but rather perform extracompression stokes, for example. Operating an engine in this fashion canextend the torque interval, thereby lowering the average torqueavailable from an engine. However, it can also increase fuel economy, atpart load, by increasing the cylinder air amount and thermal efficiency.Further, the cylinder may resume four-stroke operation by simplyeliminating any benign pumping strokes after a combustion event in themulti-stroke cylinder. Consequently, the ability to control the strokecount, e.g., 2-stroke, 4-stroke, 6-stroke, and/or 12-stroke, can enablecylinders on-demand may be used to improve fuel economy while retainingtorque capacity.

One method to control intake and exhaust valve operation during engineoperation is described in U.S. Pat. No. 6,332,446. This method providesa way of controlling electromechanical valves in a cylinder that mayreduce engine vibration in a cylinder that is operating in a cylinderdeactivation mode or in a multi-stroke mode. The method controlspressure in the deactivated cylinders by adjusting intake and exhaustvalve timing.

However, the inventors herein have recognized that the before-mentionedapproach can have several disadvantages. Namely, the approach regulatespressure in a cylinder, via valves, after a combustion event. However,the above method can result in degraded airflow control during low loadoperation. For example, multi-stroke and deactivation may be used duringlow engine load conditions to increase fuel economy. However, lowcylinder loads may reduce the inducted cylinder air amount that iscombined with injected fuel to produce combustion pressure.Electromechanical valve constraints may make it difficult to controllower cylinder air amounts because the valves may have a minimum opentime that is related to the valve inertia and to the actuator coilconstruction.

Such degraded air control may make it difficult for the before-mentionedmethod to regulate the combustion pressure and engine torque assuggested. Further, inaccuracies in the cylinder air amount may resultin increased emissions and poor drivability. Also, the method maydegrade cylinder combustion characteristics, such as burn rate orpercent of mass fraction burned, since it may not affect cylinder chargemotion, i.e., swirl and tumble, enough to compensate degraded combustioncharacteristics.

SUMMARY

One embodiment includes a method for controlling valve patterns in atleast a cylinder operating in a multi-stroke mode of an internalcombustion engine, the method comprising: operating a first valvepattern in said cylinder operating in multi-stroke mode during at leasta first engine operating condition; and operating a second valve patternin said cylinder operating in multi-stroke mode during a second engineoperating condition, said second operating condition different from saidfirst operating condition.

This method can be used to reduce the above-mentioned limitations of theprior art approaches.

By using an engine operating condition to vary a valve pattern tooperate in a cylinder, cylinder multi-stroke operation may be improved.

In one example, an engine operating with a cylinder having multipleintake and/or exhaust valves operating in a multi-stoke mode may improvecylinder air amount control by operating a valve pattern with one intakevalve that is diagonally opposed to an exhaust valve. This configurationmay improve cylinder air amount regulation because fewer than the totalnumber of available intake valves is used. When fewer valves are used toobtain a same cylinder air amount, the intake valve opening duration ofthe single intake valve can be increased to achieve the same cylinderair amount. Consequently, the increased intake valve duration may allowimproved cylinder air amount control because errors in the valveduration may be a smaller percentage of the total valve openingduration. However, during other operating conditions, multiple intakevalves can be used during the multi-stroke operation to provideincreased engine output.

In addition, the above-mentioned valve pattern operation may improvecylinder combustion characteristics at low load by increasing cylinderair charge motion. For example, the diagonally opposed pattern may beused to induce swirl in the combustion chamber and may improve lowerload combustion.

As such, several advantages can be achieved. Specifically, various ofthe approaches described herein may be used to improve engine combustionand vehicle drivability during lower load conditions. By determiningoperating patterns for cylinders operating in a multi-stoke cylindermode, low load combustion may be improved by altering cylinder airamount charge motion.

In addition, the method may reduce emissions by improving cylinder airamount control during lower load conditions. Improved cylinder airamount control may reduce rich and lean combustion events along withassociated misfires.

The above advantages and other advantages, objects and features will bereadily apparent from the following detailed description of theembodiments when taken alone or in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings,wherein:

FIG. 1 is a schematic diagram of an engine;

FIG. 2 is a flowchart of a method to determine engine torque anddelivery;

FIG. 3 is a plot of actual PMEP vs. predicted PMEP for active cylinders,determined from a polynomial with regressed coefficients;

FIG. 4 is a plot of actual FMEP vs. predicted FMEP for active cylinders,determined from a polynomial with regressed coefficients;

FIG. 5 is a plot of actual PMEP vs. predicted PMEP for inactivecylinders, determined from a polynomial with regressed coefficients;

FIG. 6 is a plot of actual FMEP vs. predicted FMEP for inactivecylinders, determined from a polynomial with regressed coefficients;

FIG. 7 is a plot of actual spark torque reduction vs. predicted sparktorque reduction determined from a polynomial with regressedcoefficients;

FIG. 8 is a plot of actual fuel mass vs. predicted fuel mass determinedfrom a polynomial with regressed coefficients;

FIG. 9 is a plot of actual cylinder air charge volume vs. predictedcylinder air charge volume determined from a polynomial with regressedcoefficients;

FIG. 10 is a flowchart to determine the number of active cylinders andvalves in an engine with electromechanically actuated valves;

FIG. 11 is an example of an initialized cylinder and valve mode matrix;

FIG. 12 is an example of a mode matrix that has been through a cylinderand valve mode selection method;

FIG. 13 is a diagram that shows engine warm-up states for cylinder andvalve mode selection;

FIG. 14 is a flowchart of a routine to determine cylinder and valvemodes based on the state of a catalyst;

FIG. 15 is a flowchart of a routine to determine cylinder and valvemodes based on operational limits;

FIG. 16 is a flowchart of a routine to determine cylinder and valvemodes based on noise, vibration, and harshness (NVH);

FIG. 17 is a flowchart of a routine to determine cylinder and valvemodes based on desired engine brake torque;

FIG. 18 is a flowchart of a routine to select cylinder and valve modes;

FIG. 19 is a valve timing sequence for a cylinder operating in analternating intake valve mode;

FIG. 20 is a valve timing sequence for a cylinder operating with phasedintake valves;

FIGS. 21 and 21 a are mechanical/electromechanical valve and cylindergrouped configuration;

FIG. 22 is another mechanical/electromechanical valve and cylindergrouped configuration;

FIG. 23 is grouped cylinder and valve control configuration of selectedvalves;

FIG. 24 is another cylinder and valve control configuration of selectedvalves;

FIG. 25 is another cylinder and valve control configuration of selectedvalves;

FIG. 26 is another cylinder and valve control configuration of selectedvalves;

FIG. 27 is another cylinder and valve control configuration of selectedvalves;

FIG. 28 is a plot of a speed dependent cylinder and valve modetransition;

FIG. 29 is a plot that shows torque capacity of a V8 engine operating ina variety of cylinder modes;

FIG. 30 is a plot of torque dependent cylinder and valve mode changes;

FIG. 31 is a plot of independent speed and torque based cylinder andvalve mode changes;

FIG. 32 is a flowchart of a routine of a method to controlelectromechanical valves during a start of an engine;

FIG. 33 a is a plot that shows representative intake valve timing at arelatively constant desired torque;

FIG. 33 b is a plot that shows representative exhaust valve timing at arelatively constant desired torque;

FIG. 34 a is a plot that shows representative intake valve timing forthe first of two different engine starts;

FIG. 34 b is a plot that shows representative intake valve timing forthe second of two different engine starts;

FIG. 35 a is a plot of representative intake valve timing during a startat sea level by the method of FIG. 32;

FIG. 35 b is a plot of representative intake valve timing during startsat altitude by the method of FIG. 32;

FIG. 36 is a representative plot of intake valve timing, desired enginetorque, and engine speed during a start of an engine by the method ofFIG. 32;

FIG. 37 is a flowchart of a method to control valve timing after arequest to stop an engine or to deactivate a cylinder;

FIG. 38 is a plot of an example of a representative intake valve timingsequence during a stop of a four-cylinder engine;

FIG. 39 is a flowchart of a method to restart electromechanical valvesin an internal combustion engine;

FIG. 40 is a plot of an example of valve trajectory regions during avalve opening and closing event;

FIG. 41 is a plot of example current during several valve restartattempts;

FIG. 42 is a flowchart of a method to improve individual cylinderair-fuel detection and control;

FIG. 43 is a plot of example simulated exhaust mass vs. crankshaft angleproduced by the method of FIG. 42;

FIG. 44 is a plot of example alternating intake/dual exhaust valveevents over a crankshaft angle interval;

FIG. 45 is a plot of example alternating intake/alternating exhaustvalve events over a crankshaft angle interval;

FIG. 46 is a plot of example single intake/alternating exhaust valveevents over a crankshaft angle interval;

FIG. 47 is a plot of example alternating intake/single exhaust valveevents over a crankshaft angle interval;

FIG. 48 is a plot of example dual intake/alternating exhaust valveevents over a crankshaft angle interval;

FIG. 49 a is a plot of example intake valve events over a crankshaftangle interval during start;

FIG. 49 b is a plot of example exhaust valve events over a crankshaftangle interval during start;

FIG. 50 a is a plot of example intake valve events over a crankshaftangle interval during start;

FIG. 50 b is a plot of example exhaust valve events over a crankshaftangle interval during start;

FIG. 51 a is a plot of example intake valve events over a crankshaftangle interval during start;

FIG. 51 b is a plot of example exhaust valve events over a crankshaftangle interval during start;

FIG. 52 a is a plot of example intake valve events over a crankshaftangle interval during start;

FIG. 52 b is a plot of example exhaust valve events over a crankshaftangle interval during start;

FIG. 53 a is a plot of example intake valve events over a crankshaftangle interval during start;

FIG. 53 b is a plot of example exhaust valve events over a crankshaftangle interval during start;

FIG. 54 is a plot showing piston trajectories and example decisionboundaries for determining the stroke of an engine during a start; and

FIG. 55 is a flowchart of a method to adjust fuel based on selectedcylinder and/or valve mode.

DETAILED DESCRIPTION

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 an exhaust valve 54. Each intake and exhaustvalve is operated by an electromechanically controlled valve coil andarmature assembly 53. Armature temperature is determined by temperaturesensor 51. Valve position is determined by position sensor 50. In analternative example, each of valves actuators for valves 52 and 54 has aposition sensor and a temperature sensor.

Intake manifold 44 is also shown having fuel injector 66 coupled theretofor delivering liquid fuel in proportion to the pulse width of signalFPW from controller 12. Fuel is delivered to fuel injector 66 by fuelsystem (not shown) including a fuel tank, fuel pump, and fuel rail (notshown). Alternatively, the engine may be configured such that the fuelis injected directly into the engine cylinder, which is known to thoseskilled in the art as direct injection. In addition, intake manifold 44is shown communicating with optional electronic throttle 125.

Distributorless ignition system 88 provides ignition spark to combustionchamber 30 via spark plug 92 in response to controller 12. UniversalExhaust Gas Oxygen (UEGO) sensor 76 is shown coupled to exhaust manifold48 upstream of catalytic converter 70. Alternatively, a two-stateexhaust gas oxygen sensor may be substituted for UEGO sensor 76.Two-state exhaust gas oxygen sensor 98 is shown coupled to exhaustmanifold 48 downstream of catalytic converter 70. Alternatively, sensor98 can also be a UEGO sensor. Catalytic converter temperature ismeasured by temperature sensor 77, and/or estimated based on operatingconditions such as engine speed, load, air temperature, enginetemperature, and/or airflow, or combinations thereof.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, andread-only memory 106, random access memory 108, 110 keep alive memory,and a conventional data bus. Controller 12 is shown receiving varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor119 coupled to a accelerator pedal; a measurement of engine manifoldpressure (MAP) from pressure sensor 122 coupled to intake manifold 44; ameasurement (ACT) of engine air amount temperature or manifoldtemperature from temperature sensor 117; and a engine position sensorfrom a Hall effect sensor 118 sensing crankshaft 40 position. In apreferred aspect of the present description, engine position sensor 118produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft from which engine speed (RPM) can bedetermined.

In an alternative embodiment, a direct injection type engine can be usedwhere injector 66 is positioned in combustion chamber 30, either in thecylinder head similar to spark plug 92, or on the side of the combustionchamber.

Referring to FIG. 2, a high level flowchart of a routine that showsengine torque calculations from desired engine brake torque throughengine output torque is shown.

As illustrated below, determination of engine torque loss for an enginecapable of cylinder deactivation and multi-stroke operation can beimproved by determining cylinder losses in both active and inactivecylinders. Typically, in conventional four-stroke engines, engineindicated torque is calculated from engine friction losses, enginepumping losses, and engine brake torque. However, when a cylinder isdeactivated, friction and pumping losses of the cylinder change.Therefore, a better estimation of total torque losses may be possible byusing both active an inactive friction and pumping losses, as describedby FIG. 2.

Furthermore, by controlling torque in individual cylinders, transitionsfrom a number of active cylinders to another number of active cylindersmay be improved by the method of FIG. 2. For example, controlling torquein individual cylinders may allow individual cylinder torque amounts tosmooth the transition from an eight-cylinder mode to a four-cylindermode. Torque in individual cylinders may be ramped, stepped, and/orfollow a predetermined trajectory during a cylinder and/or valve modechange to reduce torque disturbances. In contrast, controlling torquebased on the number of active cylinders may result in a torquedisturbance as the number of active cylinders changes from one enginerevolution to the next.

In addition, an engine operating at altitude may have different lossesdue to the operating environment. Namely, the pressure differentialacross the combustion chamber may be altered, when compared to sea leveloperation, so that the pumping efficiency may affect the engine torqueproduction. By controlling and estimating engine torque in individualcylinders (including inactive cylinders), errors introduced by a changein altitude and/or air temperature may be reduced using the method ofFIG. 2.

Also, cylinder stroke changes in multi-stroke operation, e.g.,twelve-stroke to four-stroke, can be improved. The method of FIG. 2 mayallow four-stroke operation to be resumed by simply eliminating anybenign pumping strokes and resuming a predetermined firing order after acombustion event in the multi-stroke cylinder, for example, since bothinactive and active cylinder torque losses are considered. In contrast,other methods may require cylinders to complete the current cylindercycle.

In step 210, desired engine brake torque is determined. In one example,driver demand engine brake torque is input into engine controller viaposition sensor 119, FIG. 1, and can be further adjusted based onvehicle speed, engine speed, and/or gear ratio, for example. The signalcan represent a fraction of the available engine torque at the currentengine speed. For example, at an engine speed where an engine has acapacity of 300 N-M and a driver input is fifty percent of sensor range,the desired engine brake torque can be interpreted as 150 N-M.Alternatively, the driver demand can be determined from a cruise controlsystem or a traction control system for reducing wheel slip. Afterdesired engine brake torque is determined, the routine proceeds to step212.

In step 212, engine cylinder and valve modes are selected. In oneexample, an appropriate cylinder and valve mode is selected based on thedesired engine brake torque, and other engine operating conditions andvehicle operating conditions. A detailed description of an example modeselection process is discussed in the description of FIG. 10. Thecylinder mode can indicate cylinder operation and/or valveconfiguration. For example, cylinder modes may include, but are notlimited to, V8, V6, V4, V2, I6, I5, I4, I3, I2, four-stroke, six-stroke,and twelve-stroke. Valve modes indicate valve operation and/orconfiguration in an active or inactive cylinder. For example, valvemodes may include, but are not limited to, dual intake/dual exhaust(operating two intake valves and two exhaust valves during a combustioncycle of the engine, whether it is 4, 6, or 12 stroke), dualintake/single exhaust (operating two intake valves and one exhaust valveduring a combustion cycle of the engine, whether it is 4, 6, or 12stroke), single intake/dual exhaust (operating a single intake valve andtwo exhaust valves during a combustion cycle of the engine, whether itis 4, 6, or 12 stroke), single intake/single exhaust (operating a singleintake valve and a single exhaust valve during a combustion cycle of theengine, whether it is 4, 6, or 12 stroke), alternating intake/dualexhaust (operating two intake valves during alternate cycles of acylinder while operating two exhaust valves, whether it is 4, 6, or 12stroke), dual intake/alternating exhaust (operating two intake valveswhile operating two exhaust valves during alternate cycles of acylinder, whether it is 4, 6, or 12 stroke), alternatingintake/alternating exhaust (operating two intake valves during alternatecycles of a cylinder while operating two exhaust valves during alternatecycles of an cylinder, whether it is 4, 6, or 12 stroke), singleintake/alternating exhaust (operating as single intake valve whileoperating two exhaust valves during alternate cycles of an cylinder,whether it is 4, 6, or 12 stroke), and alternating intake/single exhaust(operating two intake valves during alternate cycles of a cylinder whileoperating a single exhaust valve, whether it is 4, 6, or 12 stroke).Some example unique valve and cylinder modes are detailed in thedescription of FIGS. 21-27. Further, the alternative valve modes aredescribed in more detail with regard to FIGS. 44-48. As describedherein, the engine can be controlled so that any (or all) or groups ofthe cylinders are operated between variations of the above modes. Afterthe cylinder and valve modes have been selected, the routine proceeds tostep 214.

In step 214, engine accessory losses are determined. Typical accessorylosses include, but are not limited to, air conditioning,alternator/generator, power steering pumps, water pump, and/or vacuumpumps and combinations thereof. A total accessory loss amount can bedetermined by collectively summing individual accessory loss amountsthat are stored in tables or functions and are indexed by one or morevariables. For example, power steering pump losses can be determinedfrom a table that is indexed by ambient air temperature and steeringangle input.

Furthermore, torque loss due to power conversion and electrical valveoperation can be determined by indexing an array containing torquelosses that result from electromechanical valve operation based onengine speed, load and valve mode. The routine then continues on to step216.

In step 216, engine friction and pumping losses are determined. In oneexample, the routine determines individual cylinder losses based on thenumber of active and inactive cylinders, by looking up stored polynomialcoefficients that are based on engine operating conditions. Coefficientsare determined by analyzing cylinder pressure-volume (P-V) diagramscollected at various engine speed/load conditions. Active and inactivecylinder pressure data are collected, and then data are regressed todetermine polynomial coefficients for active and inactive cylinders.

FIGS. 3 and 4 show example regression fit data for cylinder pumping andfriction losses of an active cylinder. The data are based on thefollowing regression equations A and B:PMEP _(Act) =C ₀ +C ₁ ·V _(IVO) +C ₂ ·V _(EVC) +C ₃ ·V _(IVC-IVO) +C ₄·N  Equation A:Where PMEP_(Act) is pumping mean effective pressure, C₀-C₄ are stored,predetermined, polynomial coefficients, V_(IVO) is cylinder volume atintake valve opening position, V_(EVC) is cylinder volume at exhaustvalve closing position, V_(IVC) is cylinder volume at intake valveclosing position, V_(IVO) is cylinder intake valve opening position, andN is engine speed. Valve timing locations IVO and IVC are based on thelast set of determined valve timings.FMEP _(Act) =C ₀ +C ₁ ·N+C ₂ ·N ²  Equation B:Where FMEP_(Act) is friction mean effective pressure, C₀-C₂ stored,predetermined polynomial coefficients, and N is engine speed.

FIGS. 5 and 6 show example regression fit data for cylinder pumping andfriction losses of a deactivated cylinder. Data are based on thefollowing regression equations C and D:PMEP _(Deact) =C ₀ =C ₁ ·N+C ₂ ·N ²  Equation C:Where PMEP_(Deact) is friction mean effective pressure, C₀-C₂ arestored, predetermined polynomial coefficients, and N is engine speed.FMEP _(Deact) =C ₀ =C ₁ ·N+C ₂ ·N ²  Equation D:

Where FMEP_(Deact) is friction mean effective pressure, C₀-C₂ arestored, predetermined polynomial coefficients, and N is engine speed.

The following describes further exemplary details for the regression andinterpolation schemes. One dimensional functions are used to storefriction and pumping polynomial coefficients for active and inactivecylinders. The data taken to determine the coefficients are collected ata sufficient number of engine speed points to provide the desired torqueloss accuracy. Coefficients are interpolated between locations where nodata exists. For example, data is collected and coefficients aredetermined for an engine at engine speeds of 600, 1000, 2000, and 3000RPM. If the engine is then operated at 1500 RPM, coefficients from 1000and 2000 RPM are interpolated to determine the coefficients for 1500RPM. Total friction losses are then determined by at least one of thefollowing equations:${FMEP}_{total} = \frac{\left\lbrack {{{Numcyl}_{Act} \cdot {FMEP}_{Act}} + {{Numcyl}_{Dact} \cdot {{FMEP}_{Dact}\left( t_{deact} \right)}}} \right\rbrack}{{Numcyl}_{total}}$ orFMEP _(total)=Modfact·FMEP _(Act)+(1−Modfact)·FMEP _(Deact)Where Numcyl_(Act) is the number of active cylinders, Numcyl_(Dact) isthe number of deactivated cylinders, Modfact is the ratio of the numberof active cylinders to total number of cylinders, and FMEP_(total) isthe total friction mean effective pressure. Total pumping losses arethen determined by one of the following equations:${PMEP}_{total} = \frac{\left\lbrack {{{Numcyl}_{Act}*{PMEP}_{Act}} + {{Numcyl}_{Dactt}*{{PMEP}_{Dact}\left( t_{deact} \right)}}} \right\rbrack}{{Numcyl}_{total}}$ orPMEP _(total)=Modfact·PMEP _(Act)+(1−Modfact)·PMEP _(Dact)Where Numcyl_(Act) is the number of active cylinders, Numcyl_(Dact) isthe number of deactivated cylinders, Modfact is the ratio of the numberof active cylinders to total number of cylinders, and PMEP_(total) isthe total pumping mean effective pressure. Additional or fewerpolynomial terms may be used in the regressions for PMEP_(Act),PMEP_(Deact), FMEP_(Act), and FMEP_(Deact) based on the desired curvefit and strategy complexity.

The losses based on pressure are then transformed into torque by thefollowing equations:$\Gamma_{friction\_ total} = {{FMEP}_{total} \cdot \frac{V_{D}}{4 \cdot \pi} \cdot \frac{N/m^{2}}{\left( {{1 \cdot 10^{- 5}}{bar}} \right)}}$$\Gamma_{pumping\_ total} = {{PMEP}_{total} \cdot \frac{V_{D}}{4 \cdot \pi} \cdot \frac{N/m^{2}}{\left( {{1 \cdot 10^{- 5}}{bar}} \right)}}$Where V_(D) is the displacement volume of active cylinders.

In step 218, indicated mean effective pressure (IMEP) for each cylinderis determined, for example via the equation:${{IMEP}_{cyl}({bar})} = {\left( \frac{\Gamma_{brake} - \left( {\Gamma_{friction\_ tatal} + \Gamma_{pumping\_ total} + \Gamma_{accessories\_ total}} \right)}{{Num\_ cyl}_{Act}} \right)*\frac{4\quad\pi}{\quad V_{\quad D}}*{\frac{\left( \left. 1*\quad 10^{- 5}\quad{bar} \right) \right.}{N/\quad m^{\quad 2}} \cdot {SPKTR}}}$Where Num_cyl_(Act) is the number of active cylinders determined in step212, V_(D) is the displacement volume of active cylinders, SPKTR is atorque ratio based on spark angle retarded from minimum best torque(MBT), i.e., the minimum amount of spark angle advance that produces thebest torque amount. Additional or fewer polynomial terms may be used inthe regression based on the desired curve fit and strategy complexity.Alternatively, different estimation formats can also be used. The termSPKTR is based on the equation:${SPKTR} = \frac{\Gamma_{\Delta\quad{SPK}}}{\Gamma_{MBT}}$Where Γ_(ΔSPK) is the torque at a spark angle retarded from minimumspark for best torque (MBT), and Γ_(MBT) is the torque at MBT. In oneexample, the actual value of SPKTR is determined from a regression basedon the equation:SPKTR=C ₀ +C ₁*Δ_(spark) ² +C ₂*Δ_(spark) ² *N+C ₃*Δ_(spark) ² *IMEP_(MBT)Where C₀-C₃ are stored, predetermined, regressed polynomialcoefficients, N is engine speed, and IMEP_(MBT) is IMEP at MBT sparktiming. The value of SPKTR can range from 0 to 1 depending on the sparkretard from MBT. The correlation between estimated and actual sparktorque ratio is shown in FIG. 7. The routine then proceeds to step 220.

In step 220, individual cylinder fuel charges are determined. Anindividual cylinder fuel mass is determined, in one example, for eachcylinder by the following equation:M _(f) =C ₀ +C ₁ *N+C ₂ *AFR+C ₃ *AFR ² +C ₄ *IMEP+C ₅ *IMEP ² +C ₆*IMEP*NWhere M_(f) is mass of fuel, C₀-C₆ are stored, predetermined, regressedpolynomial coefficients, N is engine speed, AFR is the air-fuel ratio,and IMEP is indicated mean effective pressure. The correlation betweenestimated and actual fuel mass is shown in FIG. 8. As indicatedpreviously, additional or fewer polynomial terms may be used in theregression based on the desired curve fit and strategy complexity. Forexample, polynomial terms for engine temperature, air chargetemperature, and altitude might also be included. The routine thenproceeds to step 222.

In step 222, a desired air charge is determined from the desired fuelcharge. In one example, a predetermined air-fuel mixture (based onengine speed, temperature, and load), with or without exhaust gas sensorfeedback, determines a desired air-fuel ratio. The determined fuel massfrom step 220 is multiplied by the predetermined desired air-fuel ratioto determine a desired cylinder air amount. The desired mass of air isdetermined from the equation:M _(a) =M _(f) ·AFRWhere M_(a) is the desired mass of air entering a cylinder, M_(f) is thedesired mass of fuel entering a cylinder, and AFR is the desiredair-fuel ratio. The routine then proceeds to step 224.

In step 224, exhaust valve opening (EVO), intake valve opening (IVO),and exhaust valve closing (EVC) timing are determined from center pointof overlap and desired overlap. Center point of intake and exhaust valveoverlap is a reference point, in crank angle degrees, from where IVO andEVC are determined. Overlap is the duration, in degrees, that intakevalves and exhaust valves are simultaneously open. IVO and EVC aredetermined by the following equations: ${IVO} = {{CPO} - \frac{OL}{2}}$${EVC} = {{CPO} + \frac{OL}{2}}$Where CPO is center point of overlap and OL is overlap. The location ofCPO and OL are predetermined and stored in a table that is indexed byengine speed and air mass entering a cylinder. The amount of overlap andthe center point of overlap are selected based on desired exhaustresiduals and engine emissions.

Exhaust valve opening (EVO) is also determined from a table indexed byengine speed and air mass entering a cylinder. The predetermined valveopening positions are empirically determined and are based on abalancing engine blow down, i.e., exhaust gas evacuation, and loweringexpansion losses. Further, the valve timings may be adjusted based onengine coolant or catalyst temperature. The routine then proceeds tostep 226.

In step 226, intake valve closing is determined. Since EVO, EVC, and IVOare scheduled in one example, i.e., predefined looked-up locations,intake valve closing (IVC) is determined based on these predeterminedlocations and the desired mass of air entering a cylinder, from step222. The desired mass of air entering a cylinder is translated into acylinder volume by the ideal gas law:$V_{a} = \frac{M_{a} \cdot R \cdot T}{P}$Where V_(a) is the volume of air in a cylinder, M_(a) is a desiredamount of air entering a cylinder, from step 222, R is a ideal gasconstant, T is the intake manifold temperature, and P is the intakemanifold pressure. By using the ideal gas law, individual cylindervolumes be adjusted to provide the desired cylinder air amount ataltitude. Furthermore, an altitude factor may be added to regressionequations to provide additional altitude compensation.

From the determined cylinder volume V_(a), a model-based regressiondetermines a relationship between a volume of air in a cylinder andintake valve closing volume (IVC) from the equation:$V_{a} = {C_{0} + {C_{1}*\left( {V_{IVC} - V_{{Res}❘{Ti}}} \right)} + {C_{2}*{dV}_{Res}} + {C_{3}*\left( \frac{N}{1000} \right)*\left( {V_{\quad{IVC}} - V_{\quad{{Res}\quad ❘\quad{Ti}}}} \right)} + {C_{\quad 4}*\left( \frac{N}{\quad 1000} \right)*{dV}_{\quad{Res}}} + {C_{\quad 5}*\left( \frac{\quad T_{\quad i}}{\quad T_{\quad e}} \right)*\left( {V_{\quad{IVC}} - V_{\quad{{Res}\quad ❘\quad{Ti}}}} \right)}}$Where V_(a) is the volume of air inducted into the cylinder, C₀-C₅ arestored, predetermined, regressed polynomial coefficients, V_(IVC) iscylinder volume at intake valve closed, V_(RESITi) is the residualvolume evaluated at the cylinder inlet temperature, dV_(res) is aresidual pushback volume, i.e., the volume of exhaust residuals enteringthe intake manifold, N is engine speed, T_(i) is intake manifoldtemperature, and T_(e) is exhaust manifold temperature. Additional orfewer polynomial terms may be used in the regression based on thedesired curve fit and strategy complexity. The unknown value of V_(IVC)is solved from the above-mentioned regression to yield:$V_{IVC} = {V_{{Res}❘{Ti}} + \frac{\left( {V_{a} - C_{0} - {\left( {C_{2} + {C_{4} \cdot \frac{N}{1000}}} \right) \cdot {dV}_{Res}}} \right)}{C_{1} + {C_{3} \cdot \frac{N}{1000}} + {C_{5} \cdot \left( \frac{T_{i}}{T_{e}} \right)}}}$The solution of V_(IVC) is further supported by the following equationsderived from cylinder residual estimation:$V_{Res} = {V_{EVC} + \frac{\left( {V_{IVO} - V_{EVC}} \right)}{\left\lbrack {1 - {\left( \frac{V_{E}}{V_{I}} \right) \cdot \left( \frac{A_{E}}{A_{I}} \right)}} \right\rbrack}}$dV_(Res) = V_(Res) − V_(TDC)$V_{{Res}❘{Ti}} = {V_{Res} \cdot \left( \frac{T_{i}}{T_{e}} \right)}$$\frac{V_{E}}{V_{I}} = \sqrt{\frac{P_{m} + 1}{2}}$$V_{TDC} = \frac{V_{Dcyl}}{\left( {{CR} - 1} \right)}$${V(x)} = {\pi \cdot r^{2} \cdot \left( {L + \frac{s}{2} - {\frac{s}{2} \cdot {\cos(\Theta)}} - \sqrt{L^{2} - \left( {\frac{s}{2} \cdot {\sin(\Theta)}} \right)}} \right)}$Where V(x) is the cylinder volume at crank angle Θ relative to top deadcenter of the respective cylinder, L is the length of a connecting rod,s/2 is the crank shaft offset where the connecting rod attaches to thecrankshaft, relative to the centerline of the crank shaft, r is thecylinder radius, CR is the cylinder compression ratio, V_(Dcyl) iscylinder displacement volume, V_(TDC) is cylinder volume at top deadcenter, V_(E)/V_(I) is the air velocity ratio across exhaust and intakevalves, A_(E)/A_(I) is the area ratio across exhaust and intake valves,V_(Res) is the residual cylinder volume, V_(IVO) is cylinder volume atintake valve opening, V_(EVC) is cylinder volume at exhaust valveclosing, and V_(TDC) is cylinder volume at top dead center. Thus,cylinder volumes V_(EVC) and V_(IVO) are determined by solving for V(x)at the respective EVC and IVO crank angles.

Note that this is one example approach for setting valve timing andoverlap. An alternative approach could interrogate a series ofpredetermined tables and/or functions based on driver demand, enginespeed, and engine temperature to determine intake and exhaust valvetiming. The routine then proceeds to step 228.

In step 228, valve timings associated with IVO, IVC, EVO, and EVC arecompared against valve constraints. For example, the determined valvetimings are compared to a limited valve opening duration, i.e., valvetiming below a specified duration is avoided to improve valve-openingconsistency. If the determined valve timing is below a specifiedthreshold the valve timings are increased to a predetermined duration.If determined valve timings are above the specified threshold no valvetiming adjustments are made. Further, there may be other valveconstraints, such as a maximum opening duration, which can beconsidered. The routine then continues to step 230.

In step 230, final cylinder air amount is determined. This step can beperformed to account for any adjustments in cylinder air amountresulting from valve timing adjustment in step 228. In one example,cylinder inducted air amount is determined from the valve timings ofstep 228 and the equation: $\begin{matrix}{V_{adjusta} = {C_{0} + {C_{1}*\left( {V_{IVC} - V_{{Res}❘{Ti}}} \right)} + {C_{2}*{dV}_{Res}} + {C_{3}*\left( \frac{N}{1000} \right)*}}} \\{\left( {V_{IVC} - V_{{Res}❘{Ti}}} \right) + {C_{4}*\left( \frac{N}{1000} \right)*{dV}_{Res}} + {C_{5}*}} \\{\left( \frac{T_{i}}{T_{e}} \right)*\left( {V_{IVC} - V_{{Res}❘{Ti}}} \right)}\end{matrix}$Where V_(a) is determined from the same equation as in step 226, butthat uses revised valve timings. The correlation between estimated andactual cylinder air charge volume is shown in FIG. 9. Additional orfewer polynomial terms may be used in the regression based on thedesired curve fit and strategy complexity. Cylinder air mass is thendetermined from:M _(aadjust)=ρ_(int ake) ·V _(a)Where M_(aadjust) is mass of air entering a cylinder, ρ is density ofair in the intake manifold determined from the ideal gas law, and V_(a)is a volume of air inducted into the cylinder. The desired mass of fuelentering a cylinder is then determined from the equation:$M_{fadjust} = \frac{M_{aadjust}}{AFR}$Where M_(aadjust) is the desired mass of air entering a cylinder,M_(fadjust) is the desired mass of fuel entering a cylinder, and AFR isthe desired air-fuel ratio. Further, the desired mass of fuel can beadjusted here for lost fuel, unaccounted fuel that passes cylinder ringsor attaches to intake port walls, or for cylinder enleanment orenrichment based on cylinder and valve mode, or based on catalystconditions. Lost fuel is preferably based on a number of fueled cylinderevents.

In step 232, the spark angle delivered to a cylinder is determined. Inone example, the final spark angle is based on MBT spark timing, but isadjusted to deliver the desired IMEP. From the above mentioned IMEPequation, desired air-fuel ratio, M_(fadjust), engine speed, and IMEPadjusted for revised valve timings is determined. The adjusted IMEP isthen divided by the IMEP amount determined in step 218 to produce aratio of IMEP. This ratio is then substituted into the spark torqueratio regression equation of step 218 and solved for the final sparkangle. In one example, MBT spark timing is determined by the equation:SPK _(MBT) =C ₀ +C ₁ ·N+C ₂ ·N ² +C ₃ ·N ³ +C ₄ ·M _(f) +C ₅ ·M _(f) ²+C ₆ ·FDR+C ₇ ·FDR ² +C ₈ ·FDR ³Where C₀-C₈ are stored, predetermined, regressed polynomialcoefficients, N is engine speed, M_(f) is mass of fuel injected into acylinder, and FDR is fuel dilution ratio (mass of fuel)/(air massamount+residual mass amount).

This example method of torque control permits individual cylinder valvetiming and spark control in an engine capable of a variety of valve andcylinder modes without storing extensive engine maps within the torquecontrol strategy.

Referring to FIG. 10, a high level flowchart of cylinder and valve modeselection for an engine with electromechanically actuated valves isshown. Depending on mechanical complexity, cost, and performanceobjectives an engine can be configured with an array ofelectromechanical valve configurations. For example, if good performanceand reduced cost are desired, a plausible valve configuration mayinclude electromechanical intake valves and mechanically actuatedexhaust valves. This configuration provides flexible cylinder air amountcontrol while reducing the cost that is associated with higher voltagevalve actuators that can overcome exhaust gas pressure. Anotherconceivable mechanical/electrical valve configuration iselectromechanical intake valves and variable mechanically driven exhaustvalves (mechanically driven exhaust valves that can be controlled toadjust valve opening and closing events relative to a crankshaftlocation). This configuration may improve low speed torque and increasefuel economy at reduced complexity when compared to a fullelectromechanically actuated valve train. On the other hand,electromechanical intake and exhaust valves can provide greaterflexibility but at a potentially higher system cost.

However, unique control strategies for every conceivable valve systemconfiguration could be expensive and could waste valuable humanresources. Therefore, it is advantageous to have a strategy that cancontrol a variety of valve system configurations in a flexible manner.FIG. 10 is an example cylinder and valve mode selection method that canreduce complexity and yet is capable of flexibly controlling a varietyof different valve configurations with few modifications.

One example method described herein makes a set of cylinder and valvemodes available each time the routine is executed. As the steps of themethod are executed, different cylinder and valve modes may be removedfrom a set of available modes based on engine, valve, and vehicleoperating conditions. However, the method may be reconfigured toinitialize cylinder and valve modes in an unavailable state and thenmake desired cylinder and valve modes available as the different stepsof the routine are executed. Thus, various options are available for theselection of an initialization state, order of execution, and activationand deactivation of available modes.

In step 1010, row and column cells of a matrix (mode matrix)representing valve and cylinder modes are initialized by insertingnumerical 1's into all matrix row and column cells. An example modematrix is shown in FIG. 11 for an eight cylinder engine having two banksof four-cylinders each in a V-type configuration. The mode matrix is aconstruct that holds binary ones or zeros in this example, althoughother constructs can be used. The matrix can represent cylinder andvalve mode availability. In this example, the ones represent availablemodes while zeros represent unavailable modes.

The mode matrix is initialized each time the routine is called, therebymaking all modes initially available. FIGS. 21-27 illustrate somepotential valve and cylinder modes, and are described in more detailbelow. Although a matrix is shown, it is possible to substitute otherstructures such as words, bytes, or arrays in place of the matrix. Oncethe mode matrix is initialized the routine continues to step 1012.

In step 1012, some valve and/or cylinder modes that are affected byengine warm-up conditions are deactivated from the mode matrix. In oneexample, warm-up valve and cylinder mode selection is based on engineoperating conditions that determine an operating state of the engine.The description of FIG. 13 provides further details of warm-up valveand/or cylinder mode selection. The routine then proceeds to step 1014.

In step 1014, some valve and/or cylinder modes that affect engineemissions or that are affected by emissions are deactivated. Thedescription of FIG. 14 provides further details of cylinder and/or valvemode selection that is based on engine emissions. The routine thencontinues to step 1016.

In step 1016, some valve and/or cylinder modes that are affected byengine operating region and valve degradation are deactivated. Catalystand engine temperatures along with indications of valve degradation, areused in one example to determine cylinder and/or valve mode deactivationin this step. The description of FIG. 15 provides further details of theselection process. The routine then continues to step 1018.

In step 1018, some valve and/or cylinder modes that affect engine andvehicle noise, vibration, and harshness (NVH) are deactivated. Forexample, electromechanical valves can be selectively activated anddeactivated to change the number of active cylinders and therefore thecylinder combustion frequency. It can be desirable, under selectedcircumstances, to avoid (or reduce) valve and cylinder modes that canexcite vibrational frequencies or modes of a vehicle, i.e., frequencieswhere the mechanical structure has little or no damping characteristics.The valve and/or cylinder modes that affect these frequencies aredeactivated in step 1018. The description of FIG. 16 provides furtherdetails of NVH based valve and cylinder mode deactivation. The routinethen proceeds to step 1020.

In step 1020, some cylinder and/or valve modes that do not providesufficient torque to produce the desired engine brake torque aredeactivated. In this step desired engine brake torque is compared to thetorque capacity of the cylinder and valve modes contained within themode matrix. In one example, if the desired brake torque is greater thanthe torque capacity (including a margin of error, if desired) of a givencylinder and valve mode, then the cylinder and/or valve mode isdeactivated. Additional details of the torque based cylinder and valvemode selection process can be found in the description of FIG. 17. Theroutine then continues to step 1022.

In step 1022, the mode matrix is evaluated and the cylinder and valvemodes are determined. At this point, based on the criteria of steps1010-1020, deactivated cylinder and valve operating modes have been madeunavailable by writing zeros into the appropriate mode matrix cellrow/column pair. The mode matrix is searched starting from the matrixorigin (0,0) cell, row by row, to determine row and column pairscontaining ones. The last matrix row/column containing a value of onedetermines the valve and cylinder mode. In this way, the design of themode matrix and the selection process causes the fewest number ofcylinders and valves to meet the control objectives.

If a cylinder and/or valve mode change is requested, that is, if themethod of FIG. 10 determines that a different cylinder and/or valve modeis appropriate since the last time the method of FIG. 10 executed, thenan indication of an impending mode change is indicated by setting therequested mode variable to a value indicative of the new cylinder and/orvalve mode. After a predetermined interval, the target mode variable isset to the same value as the requested mode variable. The requested modevariable is used to provide an early indication to peripheral systems ofan impending mode change so that those systems may take action beforethe actual mode change. The transmission is one example where suchaction is taken, as described in FIG. 28. The actual cylinder and/orvalve mode change is initiated by changing the target mode variable.Furthermore, the method may delay changing requested and target torquewhile adjusting fuel to suit the new cylinder and/or valve mode bysetting the MODE_DLY variable. Cylinder and/or valve mode changes areinhibited while the MODE_DLY variable is set.

The chosen valve and cylinder mode is then output to the torquedetermination and delivery routine. The cylinder and valve modeselection routine is then exited.

In addition, the cylinder and valve mode matrix structure can takealternate forms and have alternate objectives. In one example, insteadof writing ones and zeros to the cells of the matrix an alternateembodiment might write numbers to the matrix that are weighted by torquecapacity, emissions, and/or fuel economy. In this example, selection ofthe desired mode might be based on the values of the numbers writteninto the matrix cells. Further, modes that define the axis of the matrixdo not have to be in increasing or decreasing torque amounts; fueleconomy, power consumption, audible noise, and emissions are a fewadditional criteria that may be used to define the structure of the modecontrol matrix organization. In this way, the matrix structure can bedesigned to determine cylinder and valve modes based on goals other thanfewest cylinders and valves.

Also, the method of FIG. 10 may be configured to determine operatingconditions of a valve, valve actuator, engine, chassis, electricalsystem, catalyst system, or other vehicle system. The before-mentionedoperating conditions may be used to determine a number of activecylinders, number of active valves, valve patterns, cylinder strokes ina cylinder cycle, cylinder grouping, alternate valve patterns, and valvephasing desired. Determining a variety of operating conditions andselecting an appropriate cylinder and valve configuration may improveengine performance, fuel economy, and customer satisfaction.

In one example, at least the following two degrees of freedom can beused to regulate torque capacity of an engine:

-   -   (1) the number of cylinders carrying out combustion; and    -   (2) the number of valves operating in each cylinders

Thus, it is possible to increase the resolution of torque capacitybeyond that obtained by simply using the number of cylinders.

Furthermore, the method of FIG. 10 can switch between cylinder and valvemodes during a cycle of the engine based on engine operating conditions.

In another example, an eight-cylinder engine operates four-cylinders infour-stroke mode and four-cylinders in twelve-stroke mode, all cylindersusing four valves in each cylinder. This mode may generate the desiredtorque and a level of increased fuel efficiency by reducing the numberof active cylinders and by operating the active cylinders at a higherthermal efficiency. In response to a change in operating conditions, thecontroller might switch the engine operating mode to four-cylindersoperating in a four-stroke mode and using two valves in each cylinder.The remaining four-cylinders might operate in twelve-stroke mode withalternating exhaust valves.

In another example, under other operating conditions, some cylinders areoperated with fuel injection deactivated, and others are operated with 4valves active per cylinder. This mode may generate the desired torquewhile further increasing fuel efficiency. Also, the exhaust valves inthe cylinders operating in twelve-stroke mode may cool due to thealternating pattern. In this way, the method of FIG. 10 permits anengine to change the number of active cylinders, number of strokes in acycle of a cylinder, number of operating valves, and the valve patternbased on operating conditions and the mode matrix calibration anddesign.

Because an engine with electromechanical valves is capable of operatingdifferent cylinders in different modes, e.g., half the number ofavailable cylinders in four-stroke and the remainder of cylinders insix-stroke, a cycle of an engine is defined herein as the number ofangular degrees over which the longest cylinder cycle repeats.Alternatively, the cycle of a cylinder can be individually identifiedfor each cylinder. For example, again, where an engine is operating withcylinders in both four and six stroke modes, a cycle of the engine isdefined by the six-stroke cylinder mode, i.e., 1080 angular degrees. Thecylinder and valve mode selection method described by FIG. 10 may alsobe used in conjunction with a fuel control method to further improveengine emissions. One such fuel control method is described by theflowchart illustrated in FIG. 55.

Referring to FIG. 11, an example of an initialized cylinder and valvemode matrix for a V8 engine with electromechanical intake and exhaustvalves is shown. The x-axis columns represent a few of potentially manyvalve modes for a cylinder with four valves. Dual intake/dual exhaust(DIDE), dual intake/alternating exhaust (DIAE), alternating intake/dualexhaust (AIDE), and alternating intake/alternating exhaust (AIAE) areshown from left to right, from higher to lower torque capacity. They-axis rows represent a few of potentially many cylinder modes for a V8engine. The cylinder modes with more cylinders begin at the bottom andend at the top with fewer cylinders, from higher to lower torquecapacity.

In this example, the mode matrix is advantageously constructed to reducesearch time and mode interpretation. The intersection of a row andcolumn, a cell, identifies a unique cylinder and valve mode. Forexample, cell (1,1) of the mode matrix in FIG. 12 represents V4 cylindermode and dual intake/alternating exhaust (DIAE) valve mode. The modematrix is organized so that engine torque capacity in the cylinder/valvemode decreases as the distance from the origin increases. The reductionin torque capacity is greater by row than by column because the numberof active cylinders per engine cycle decreases as the row numberincreases, whereas the different valve modes reduce the engine torque bya fraction of a cylinder torque capacity.

Since the mode matrix construction is based on valves and cylinders, itnaturally allows cylinder and valve modes to be defined that determinethe number of active cylinders and valves as well as the cylinder andvalve configuration. In addition, the mode matrix can identify cylinderand valve configurations that group cylinders and that have uniquenumbers of operating valves and valve patterns. For example, the modematrix can be configured to provide half of active cylinders with twoactive valves and the other half of active cylinders with three activevalves. Also, the mode matrix supports selection of multi-stroke modes.Multi-stroke operation generally includes a combustion cycle of greaterthan a four stroke combustion cycle. As described herein, multistrokeoperation includes greater than four stroke combustion, and variation ofthe number of strokes in the combustion cycle, such as, for example,variation between four-stroke, six-stroke, and/or twelve-stroke.

Further, different cylinders may be made active for a single cylindermode, e.g., in a four-cylinder engine I2 cylinder mode may be producedby cylinders 1-4 or 2-3, by defining and selecting from two uniquematrix cells.

Any of the cylinder and valve modes represented in the mode matrix canbe deactivated with the exception of the cylinder and valve mode that islocated in the (0,0) cell. Cell (0,0) is not deactivated so that atleast one mode is available.

Referring to FIG. 12, an example of a matrix that has been through thecylinder and valve mode selection process is shown. The figure shows thezeros in the matrix cells that were initially set to ones in the modematrix initialization, step 1010. Also, in the steps of the method ofFIG. 10, when a cylinder and valve mode is deactivated, cylinder andvalve modes of lesser torque capacity are also deactivated. For example,cell (1,2) has the higher torque capacity of the cells containing zeros.Based on the cylinder selected and valve mode selection criteriadescribed above, cell (1,1) is selected as the current cylinder andvalve mode, i.e., V4-dual intake/alternating exhaust (DIAE). This canreduce search time of the matrix if searching ceases after a zero isencountered in the matrix.

Referring to FIG. 13, a diagram of the state machine that selectscylinder and valve modes based on warm-up conditions is shown. Fourstates are shown but fewer or additional states are possible. State1316, the cold state, is the default state entered when the cylinder andvalve mode selection routine is executed for the first time (e.g., aftera start). Engine and/or vehicle operating conditions thereafterdetermine the occupied state. Further, the arrows connecting states1310-1316 designate operational conditions that trigger a state change,transferring state control from one state to another. For example, uponreceiving a key on indication the cold state 1316 is entered. Vehicleand engine operating conditions are then determined, and if conditionspermit the operational state is changed. A representative condition thattriggers state change from the cold state 1316 to the warm stabilizedstate 1310 via arrow 1320 is:

-   -   If(((ECT>ECTSTBL)&(CAT>CATWRM)) or ((ECT>ECTWRM)&(CAT>CATSTBL)))        Where ECT is measured or inferred engine temperature, ECTSTBL is        a predetermined engine temperature that indicates the engine is        at a warm operating temperature, CAT is a measured or inferred        catalyst temperature, CATWRM is a predetermined catalyst        temperature that indicates at least a partially warm catalyst        system, ECTWRM is a predetermined engine temperature that        indicates that the engine is warm but not at a stabilized        operating temperature ECTSTBL, and CATSTBL is a predetermined        catalyst temperature that indicates that the catalyst is at a        temperature that permits efficient catalytic reactions.

Similar rule sets control the transitions between the other states.Thus, if the statement is true, the cold state 1316 is exited and thewarm stabilized state 1310 is entered. Contained within each state is apredetermined state matrix of the same dimensions as the mode matrix.The predetermined state matrix can contain ones and zeros. When in agiven state any zeros entered in the predetermined state matrix arecopied into the mode matrix. Each time the mode selection routine isexecuted there is potential to change states. In this way, the differentwarm-up states update the mode matrix. Further, calibration ofpredetermined state matrices allows catalyst temperature and enginetemperature to determine active and inactive cylinder and valve modes.That is, engine and catalyst temperatures can determine the number ofactive cylinders and the number of strokes in the active cylinders, plusthey can determine the number and configuration or pattern ofoperational valves.

Warm-up cylinder and valve mode selection determination based onoperational conditions of an engine are not constrained to enginetemperature and catalyst temperature. Transitions between operatingstates may also be determined by engine oil temperature, ambient airtemperature, barometric pressure, humidity, and a number of fueledcylinder events after a start, such as a number of combustion events.

Although engine and catalyst temperature provide an indication of engineoperating conditions, conditions of an electromechanical valve canprovide additional information and in some cases a basis for cylinderand valve mode changes. For example, armature temperature determined bysensor 50 (or estimated) may be included into the above-mentionedrepresentative condition that triggers a state change. Further, thenumber of valve operations, time since start, valve operating time,valve current, valve voltage, power consumed by the valve, valveimpedance sensing devices, combinations thereof, and/or sub-combinationsthereof can augment (or supplant) the armature temperature sensor byproviding additional operating conditions of a valve. Consequently,operating conditions of an electromechanical valve can be used todetermine the number of active cylinders and/or the number of strokes inthe active cylinders, plus they can optionally be used to determine thenumber and configuration or pattern of operational valves. These valveoperating conditions may be included with engine and catalyst conditionsin the state transition logic or they can comprise state transitionlogic without engine and catalyst operating conditions.

Selecting valve patterns, e.g., opposed intake and/or exhaust valves ordiagonally opposed intake and exhaust valves, may also be based onwarm-up conditions, cylinder stroke mode, and number of active cylindersby the state machine. This is accomplished by leaving desired valvepatterns, cylinder stroke modes, and cylinder modes active in a givenwarm-up state. Then the remaining selection criteria of FIG. 2 candetermine the cylinder mode, number of active valves, active valvepattern, and cylinder stroke mode by applying the conditionalconstraints of steps 1014-1022 of FIG. 10.

Selection of electromechanical valves operation during the enginewarm-up in this way can improve engine operation in a number of ways,such as, for example, by operating all cylinders of an engine with afewer number of valves. One example of such an option would be a V8 withfour electromagnetic valves per cylinder operated with eight cylindersand two valves per cylinder. Not only can such operation increase fueleconomy (by saving electrical energy by reduced valve current), butengine noise, vibration, and harshness (NVH) can also be reduced sinceengine torque peaks are closer together. Further, valve powerconsumption at low temperature increases while power supply capacity maydecrease. Therefore, selecting a fewer number of valves during a lowtemperature condition (such as, for example, during an engine start) canmake more current available to the engine starter so that longer enginecranking (rotating the engine until the engine is rotating under its ownpower) and higher cranking torque is possible without depleting batterycapacity.

The state machine of FIG. 13 can be further configured to accommodatewarm-up states that are entered based on operating conditions of atransmission. For example, transmission oil temperature, gear selectorposition, or estimated transmission torque losses may also beincorporated into warm-up state determination logic and used to selectengine and valve modes.

Continuing with the remaining transitions of FIG. 13, the transitionfrom cold state 1316 to the warm stabilized state 1310 is performed if:

(((ECT>ECTSTBL)&(CAT>CATWRM)) or ((ECT>ECTWRM)&(CAT>CATSTBL)))

The transition from cold state 1316 to the warm state 1312 is performedif:

(((ECT>ECTWRM)&(CAT>CATCOL)) or((ECT>ECTCOL)&(CAT>CATWRM)))&((ECT<ECTSTBL)&(CAT<CATSTBL))

The transition from cold state 1316 to the cool state 1314 is performedif:

(((ECT>ECTCOL)&(CAT>CATCLD)) or((ECT>ECTCLD)&(CAT>CATCOL)))&((ECT<ECTWRM)&(CAT<CATWRM))

The transition from cool state 1314 to warm state 1312 is performed if:

(((ECT>ECTWRM) & (CAT>CATCOOL)) or ((CAT>CATWRM) & (ECT>ECTCOL)))

The transition from warm state 1312 to warm stabilized state 1310 isperformed if:

(((ECT>ECTSTBL) & (CAT>CATWRM)) or ((CAT>CATSTBL) & (ECT>ECTWRM)))

The transition from warm stabilized 1310 to warm 1312 is performed if:

((ECT<ECTSTBL) & (CAT<CATSTBL))

The transition from warm 1312 to cool 1314 is performed if:

((ECT<ECTWRM) & (CAT<CATWRM))

And finally, the transition from cool 1314 to cold 1316 is performed if:

((ECT<ECTCOL) & (CAT<CATCOL))

Where CATCOL is a catalyst temperature threshold that identifies a coolcat temp (e.g., 400 deg F.), ECTCOL is a engine temperature thresholdthat identifies a cool engine (e.g., 110 deg F.), CATCLD is a catalysttemperature threshold that identifies a cold cat (e.g., 70 deg F.), andECTCLD is a temperature that identifies a cold engine temperature (e.g.,70 deg F.).

Referring to FIG. 14, a method to deactivate cylinder and valve modesfrom the mode matrix based on catalyst operating conditions (forexample, catalyst state) is shown. In one example, an oxidant storagestate (such as an amount of oxidants stored) is used. In one example,oxygen is the primary oxidant. In one approach, catalyst temperature canbe used in determining a catalyst operating condition. However, inanother example, catalyst temperature (even though a factor indetermining an oxidant storage state) is not explicitly used todetermine cylinder and valve modes since this feature can be captured inthe warm-up cylinder and valve mode selection, see FIG. 13. The methodevaluates each cylinder and/or valve mode represented in the mode matrixand deactivates selected modes based on the evaluation.

In steps 1410 and 1412, Catalyst storage capacity (such as a maximumoxidant storage availability at the current operating conditions) andoxidant storage amount are determined. In one example, these can bedetermined using the method in accordance with U.S. Pat. No. 6,453,662,which is hereby fully incorporated by reference.

In one example, catalyst capacity is determined after filling thecatalyst with oxidants by running the engine with a lean air/fuel ratiofor an extended period of time. After the catalyst is filled, theair/fuel ratio provided to the engine is made rich. The pre-catalystoxygen sensor 76 detects the rich air/fuel condition in the exhaustalmost immediately. However, because the HC and CO produced by the richengine air/fuel ratio reacts with the stored oxidants in the catalyst,there is a time delay until the post-catalyst oxygen sensor 98 detects arich air/fuel ratio in the downstream exhaust. The length of the timedelay is indicative of the oxidant storage capacity of the catalyst.Based upon the measured time delay, a deterioration factor between 0 and1 (0 representing total deterioration and 1 representing nodeterioration) is calculated. Alternatively, the method could be used inreverse, i.e., the catalyst could be depleted due to extended richoperation, after which the air/fuel ratio would be switched to leanoperation. Similar to the original method, the length of the time delayuntil the post-catalyst sensor 98 registered a change in state would beindicative of the catalyst storage capacity. Also, the duration of delaycan be affected by catalyst space velocity, air flow, temperature, etc.,and these parameters can be therefore included in the calculation. Theroutine then proceeds to step 1414.

In step 1414, an engine emissions amount is determined by looking upstored empirical emissions concentrations of HC, CO, and NO_(x) at thecurrent engine speed/load operating conditions. These concentrations canbe integrated over time to determine a mass weight of each constituent.Further, functions that represent spark advance and air-fuel modifiersalter emissions concentrations, and can be included. Alternatively,emissions sensors may be employed to make a direct measurement of aconstituent of interest. Still further, combinations of estimates andmeasurements can also be used. The routine then proceeds to step 1416.

In step 1416, estimated catalyst oxidant storage capacity, CAT_CAP, iscompared to a predetermined matrix of oxidant catalyst storage capacityamounts, CAT_STOR. In other words, each cylinder and valve mode may havea unique desired catalyst storage capacity that is compared to theestimated catalyst oxidant storage capacity. If the current catalystoxidant storage capacity is above the amount stored in the predeterminedcatalyst storage matrix (which can represent a desired catalyst oxidantcapacity for a selected cylinder and/or valve mode) the routine proceedsto step 1418. Otherwise, the routine continues to step 1420.

In step 1420, cylinder and valve modes are deactivated based on thecatalyst oxidant storage capacity. Cylinder and valve modes aredeactivated based on the comparison of catalyst oxidant storage capacityverses the predetermined matrix of catalyst oxidant storage from step1416. In other words, if current catalyst oxidant storage capacity isbelow a predetermined amount for a specific cylinder and valve mode,then the cylinder and valve mode is deactivated. In this way, cylinderand valve mode are determined, in part, by catalyst oxidant storagecapacity.

In step 1418, an amount of estimated stored oxidants, CAT_OXY, iscompared to a predetermined matrix of oxidant catalyst storage capacityamounts, CAT_STOR, from step 1416. If the current catalyst oxidantstorage capacity is greater than X % of the amount stored in thepredetermined catalyst storage matrix the routine proceeds to step 1422.The value of X may be determined by indexing an array based on enginespeed, engine air amount, and vehicle speed.

To estimate the amount of oxidants, CAT_OXY, that are actuallyadsorbed/desorbed by the catalytic converter, (which can be done on aper brick basis) this estimation depends on several factors, includingthe volume of the catalytic converter 70, the flow rate of oxidants inthe exhaust manifold 48, the percentage of the catalytic converter thatis already full of oxidants, and other physical and operationalcharacteristics of the catalytic converter. The change in the amount ofoxidants stored in the catalytic converter 70 between two preset times(ΔT) is estimated based on the following model: $\begin{matrix}\begin{matrix}{{\Delta\quad O_{2}} = {C_{1}*C_{2}*C_{3}*C_{4}}} \\{\left\lbrack {K_{a}*\left( {1 - \frac{{Stored}\quad O_{2}}{{Max}\quad O_{2}}} \right)^{N_{1}}*\left( \frac{O_{2}\quad{Flow}\quad{Rate}}{{Base}\quad{Value}} \right)^{Z_{1}}*{Cat}\quad{Vol}*\Delta\quad T} \right\rbrack}\end{matrix} & (A)\end{matrix}$

for Oxygen being adsorbed $\begin{matrix}\begin{matrix}{{\Delta\quad O_{2}} = {C_{1}*C_{2}*C_{3}*C_{4}}} \\{\left\lbrack {K_{d}*\left( \frac{{Stored}\quad O_{2}}{{Max}\quad O_{2}} \right)^{N_{2}}*\left( \frac{O_{2}\quad{Flow}\quad{Rate}}{{Base}\quad{Value}} \right)^{Z_{2}}*{Cat}\quad{Vol}*\Delta\quad T} \right\rbrack}\end{matrix} & (B)\end{matrix}$

for Oxygen being desorbed

As indicated above, Equation (A) is used to calculate the change inoxidant storage in the catalytic converter if the catalyst is in anadsorption mode and Equation (B) is used if the catalyst is in adesorption mode.

In Equations (A) and (B), the variables C₁, C₂, and C₃ are assignedvalues to compensate for various functional and operationalcharacteristics of the catalytic converter. The value of C₁ isdetermined according to a mathematical function or look-up table basedon the catalyst temperature. One embodiment uses a mathematical functionthat illustrates that a catalytic converter is most active when thecatalyst is hot and least active when it is cold. The catalysttemperature can be determined according to several different methodsthat are well-known to those of skill in the art, including by acatalyst temperature sensor.

The value of C₂ in Equations (A) and (B) is determined based on thedeterioration of the catalytic converter. The deterioration of thecatalytic converter can be determined by a variety of well-knownmethods, including, for example, inferring such age or deteriorationfrom the vehicle's total mileage (recorded by the vehicle's odometer) ortotal amount of fuel used over the vehicle's lifetime. Further, acatalytic deterioration factor can be calculated according to one of thepreferred methods described hereinabove.

The value of C₃ is determined by a mathematical function or map based onthe air mass flow in the exhaust manifold 48 which can be measured orinferred. The mathematical function used to assign values to C₃ dependson the mass airflow rate in the induction manifold 44. Theadsorption/desorption efficiency of the catalyst decreases as the massflow rate increases.

The C₄ value is read from a two-dimensional look-up table of adaptiveparameters. The primary index to the look-up table is air mass flow. Foreach air mass flow, there are two C₄ values—one for when the catalyst isadsorbing oxidants (equation (A)) and one for when the catalyst isdesorbing oxidants (equation (B)). Thus, the value of C₄ used inequations (A) and (B) above varies from time to time with the determinedair mass flow.

In Equation (A), the value of k_(a) represents the maximum adsorbingrate of the catalytic converter in terms of grams of oxidants per secondper cubic inch. Similarly, in Equation (B), the value of k_(d)represents the maximum desorbing rate of the catalytic converter interms of grams of oxidants per second per cubic inch. The values ofk_(a) and k_(d) are pre-determined based on the specifications of theparticular catalytic converter being used.

The value for Max O₂ in both Equation (A) and Equation (B) representsthe maximum amount of oxidants that the catalyst 70 is capable ofstoring in terms of grams. This is a constant value that ispre-determined according to the specifications of the particularcatalytic converter used in the system. The value for Stored O₂ inEquations (A) and (B) represents the previously-calculated currentamount of oxidants stored in the catalytic converter 70 in terms ofgrams. The value for Stored O₂ is read from RAM 108.

The value for O₂ Flow Rate in Equation (A) and Equation (B) representsthe cylinder air amount. The Base Value in Equation (A) and Equation (B)represents the oxygen flow rate where K_(d) and K_(a) were determinedand it is (PPM O₂ of input gas)*(volumetric flow rate)*(density of O₂).

The Cat Vol parameter in Equation (A) and Equation (B) represents thetotal volume of the catalytic converter in terms of cubic inches. Thisvalue is pre-determined based on the type of catalytic converter beingused. The value ΔT in both equations represents the elapsed time inseconds since the last estimation of the change in oxidant storage inthe catalyst.

Finally, the values of N₁, N₂, Z₁, and Z₂ are exponents that express theprobability of desorption/adsorption and they are determined byexperimentally measuring rates of adsorption/desorption at given levelsof storage and flow. The exponents are regressed from measurements andcan be used to describe linear to sigmoid probabilities.

After the change in estimated oxidant storage in the catalyst 70 iscalculated according to Equation (A) or Equation (B), the running totalof the current oxidant storage maintained in RAM memory 108 is updatedaccordingly. Specifically, the amount of oxidants either adsorbed ordesorbed is added/subtracted to the running total of oxidant storage,which is maintained in RAM memory 108.

If the current catalyst oxidant storage capacity is not greater than X %of the amount stored in the predetermined catalyst storage matrix, theroutine continues and exits, signifying that the catalyst has a desiredoxidant storage capacity and that a desired amount of the storagecapacity remains for storing oxidants.

In step 1422, cylinder and valve modes are deactivated based on theamount of oxidants stored in the catalyst. Cylinder and valve modes aredeactivated based on the comparison of oxidants stored in a catalyst toa percentage of an amount stored in the predetermined catalyst storagematrix. In other words, if the amount of oxidants stored in a catalystare greater than a percentage of a predetermined amount then thosecylinder and valve modes that are greater than the desired amount aredeactivated. For example, if a catalyst has a predetermined oxidantstorage capacity of 0.0001 gm and has a desired oxidant storage capacityof 60% or less of the predetermined oxidant storage capacity then thecylinder and valve mode will be deactivated if the stored oxidant amountis greater than 0.00006 gm.

An alternative to the method of FIG. 14 is to recognize thatdeactivation of cylinder and valve modes can affect engine feed gasemissions. Therefore, cylinder and valve modes may be selected to alterthe catalyst state. That is, deactivating certain cylinder and valvemodes can constrain engine feed gas emissions altering the gasconcentrations that enter the catalyst. For example, a V8 engineoperating in V4 cylinder and dual intake/dual exhaust mode may producehigher levels of oxidants as compared to a V8 cylinder mode due tohigher in cylinder temperatures and pressures. If a catalyst oxidantstorage capacity is less than desired, V4 cylinder mode could bedeactivated in an effort to reduce NOx emissions.

In addition, engine fuel may be adjusted before and during acylinder/valve mode change to further affect the amount of oxidantsstored in a catalyst. For example, if an engine is operating in an eightcylinder mode and mode selection criteria permits switching to anothermode, four-cylinder mode for example, fuel may be added or subtractedfrom the base fuel amount to bias the total fuel amount in a rich orlean direction, before the mode change is initiated, to precondition thecatalyst for the mode change. Further, during and after a mode change,fuel may be added or subtracted from the base fuel amount to bias thetotal fuel amount in a rich or lean direction. The fuel adjustments mayprovide compensation for gas constituent changes that may occur due todifferent cylinder air amounts.

In one example embodiment, advantageous operation can be obtained for anengine with electromechanical valves that is first operating in a firstoperating mode with a first valve and/or cylinder configuration (e.g., afirst group of cylinders operating with a first number of valves and asecond group operating with a second number of valves, or some cylindersin 4-stroke and some cylinders in 12 stroke mode, or some cylindersdeactivated and remaining cylinders having differing number of activevalves, or combinations or subcombinations thereof), and transitions tooperating in a second operating mode with a second valve and/or cylinderconfiguration. And, before and/or during the transition, the exhaust gasmixture air-fuel ratio is temporarily biased lean or rich toprecondition the exhaust system (by, for example, changing the air-fuelmixture in one or more cylinders carrying out combustion).

Referring to FIG. 15, a flowchart of a method to deactivate cylindermodes (from available modes, for example) based on engine and valveoperational limits is shown. The method evaluates engine and catalysttemperatures to determine which available cylinder and valve modesshould be deactivated. Further, if valve degradation is indicated themethod deactivates cylinder and valve modes influenced by thedegradation, with the exception of the cylinder and valve mode in cell(0,0) of the mode matrix, if desired.

In step 1510, engine operating conditions are determined. Enginetemperature sensor 112 and catalyst brick temperature 77 are measured.Alternatively, the temperatures may be inferred. In addition, exhaustvalve temperature can be inferred from empirical data based on enginetemperature, exhaust residuals, engine speed, engine air amount, andspark advance. The routine then proceeds to step 1512.

In step 1512, catalyst temperature, CAT_TEMP, is compared to apredetermined variable CAT_tlim. If the catalyst temperature is greaterthan CAT_tlim the routine proceeds to step 1514. If catalyst temperatureis less than CAT_tlim then the routine proceeds to step 1516.

In step 1514, cylinder and valve modes are deactivated based onpredetermined matrix, CAT_LIM_MTX. The matrix has the same dimension asthe mode matrix, i.e., the matrices have the same number of elements.Within CAT_LIM_MTX, the cylinder and valve modes that produce highertemperatures are deactivated. The deactivated modes are then copied fromthe CAT_LIM_MTX to the mode matrix. For example, if a measured orinferred catalyst temperature is higher than desired for a V8 engine,partial cylinder modes, V4, six-stroke, and V2 are deactivated.Deactivating the partial cylinder modes lowers exhaust temperatures bydecreasing the load per cylinder at the same desired torque. The routinethen proceeds to step 1516.

In step 1516, engine temperature, ENG_TEMP, is compared to apredetermined variable ENG_tlim. If the engine temperature is greaterthan ENG_tlim the routine proceeds to step 1518. If the enginetemperature is less than ENG_tlim then the routine proceeds to step1520.

In step 1518, cylinder and valve modes are deactivated based onpredetermined matrix, ENG_LIM_MTX, where the matrix has the samedimension as the mode matrix, i.e., the matrices have the same number ofelements. Within ENG_LIM_MTX the cylinder and valve modes that producehigher temperatures are deactivated. The deactivated modes are thencopied from the ENG_LIM_MTX to the mode matrix. For example, if ameasured or inferred catalyst temperature is higher than desired for aV8 engine, partial cylinder modes, V4, six-stroke, and V2 aredeactivated. Deactivating the partial cylinder modes can lower exhausttemperatures by decreasing the load per cylinder at the same desiredtorque. The routine then proceeds to step 1520.

In step 1520, the inferred exhaust valve temperature, EXH_vlv_tmp, is toa predetermined variable EXH_tlim. If the inferred exhaust valvetemperature is greater than EXH_tlim the routine proceeds to step 1522.If the inferred exhaust valve temperature is less than the EXH_tlim thenthe routine proceeds to step 1524.

In step 1522, cylinder and valve modes are deactivated based onpredetermined matrix, EXH_LIM_MTX, where the matrix has the samedimension as the mode matrix, i.e., the matrices have the same number ofelements. Within EXH_LIM_MTX the cylinder and valve modes that producehigher temperatures are deactivated. The deactivated modes are thencopied from the ENG_LIM_MTX to the mode matrix. For example, if ameasured or inferred exhaust valve temperature is higher than desiredfor a V8 engine, partial cylinder modes, V4, six-stroke, and V2 aredeactivated and the exhaust valves operate in an alternating mode.Deactivating the partial cylinder modes lowers exhaust temperatures bydecreasing the load per cylinder while alternating valves facilitatesheat transfer between the inactive exhaust valve and the cylinder head.The routine then proceeds to step 1524.

In step 1524, valve degradation is evaluated. The valve degradation canbe indicated in a number of ways that may include but are not limitedto: valve position measurements, temperature measurements, currentmeasurements, voltage measurements, by inference from oxygen sensors, orby an engine speed sensor. If valve degradation is detected, a variable,VLV_DEG, is loaded with the number of cylinders with degraded valves anda cylinder identifier, CYL_DEG, is loaded with the latest cylindernumber where the degraded valve is located, in step 1528. If valvedegradation is present, the routine continues to step 1526. If valvedegradation is not indicated the routine exits.

In step 1526, cylinder and valve modes that are affected by valvedegradation are deactivated, which can include deactivating thecylinder(s) with the degraded valve(s). Specifically, the cylinder inwhich the degraded valve is located, CYL_DEG, is an index into a matrix,FN_DEGMODES_MTX, that contains cylinder modes that are affected by thecylinder that contains the degraded valve. The routine then deactivatesthe cylinder modes that are identified by the FN_DEGMODES_MTX. However,in one example, the cylinder mode of row zero is not deactivated so thatthe engine is capable of delivering torque from at least some (or all)cylinders with non-degraded valves when requested. In addition, if morethan one cylinder has degraded performance due to degraded valveperformance, i.e., VLV_DEG is greater than one, the cylinder modecorresponding to row zero is the single active cylinder mode. In thisway, a cylinder identified to have degraded performance causes affectedcylinder modes to be deactivated, which may include disablingcombustion, fuel injection, and/or ignition plug activation in thecylinders with degraded valves. Thus, fuel and/or spark can bedeactivated in cylinders with degraded valve performance.

Valve performance degradation may also be compensated in step 1526.Valve temperature is sensed by temperature sensor 50, but additionalvalve operating conditions may be determined as well. For example, valvevoltage, impedance, and power consumption may be sensed or inferred.These parameters may be compared to predetermined target amounts to formerror amounts that are then used to adjust an operating parameter of avehicle electrical system. For example, if ambient air temperatureincreases and a voltage amount, measured or inferred, at a valve islower than desired, a signal may be sent to the vehicle electricalsystem to increase the supply voltage. In this way, operating conditionsof the valve may be used to adjust an operating condition of a vehicleelectrical system so that valve operation is improved. The routine thenproceeds to step 1530.

In step 1530, operating conditions of a vehicle electrical system areassessed. If electrical system available power, available current,and/or available voltage is below a predetermined amount or is degraded,the routine proceeds to step 1532. Furthermore, if an externalelectrical load, e.g., a computer or video game powered by the vehicleelectrical system, or an ancillary, lower priority electrical load,e.g., a vehicle component, such as an air pump or fan, is loading thevehicle electrical system more than a predetermined amount or more thana fraction of the total available electrical system capacity, theroutine proceeds to step 1532. The routine then proceeds to exit.

In step 1532, cylinder and valve modes are deactivated based onelectrical system operating conditions. Copying zeros from selectedmatrices into the mode matrix deactivates cylinder and valve modes. Ifelectrical system available power, available current, and/or availablevoltage are below a first set of predetermined amounts, matrix FNVLVREDzeros are copied into the mode matrix. In this example, the zerosrestrict valve operation to the number of engine cylinders with twooperational valves per cylinder. If the above-mentioned electricalparameters are below a second set of predetermined amounts, matrixFNCYLRED zeros are copied into the mode matrix. In this example, thezeros restrict valve operation to a reduced number of active cylindersand a reduced number of valves in active cylinders.

Further, if power to external or ancillary loads exceeds predeterminedamounts, controlling a power switch, e.g., a relay or transistordeactivates power to these devices. The combination of deactivatingcylinder and valve modes along with reducing the affect of external andancillary electrical loads can improve likelihood of starting duringconditions of reduced electrical system capacity. For example, duringcold ambient temperatures, engine friction increases and battery powermay be reduced. By deactivating lower priority electrical loads andselecting a reduced number of active cylinders and valves, additionalelectrical power is available for an engine starter and active valvesduring starting. In addition, vehicle range may be increased ifelectrical system performance degrades during engine operation bydeactivating lower priority electrical loads and reducing activecylinders and valves.

Referring to FIG. 16, a flowchart of a method to deactivate cylindermodes based on frequencies of modal vibration of a vehicle chassis andcomponents. The method evaluates engine speed and predicts future enginespeed so that excitation of modal frequencies of the vehicle chassis andcomponents can be reduced. Components whose modal frequencies aredesirable to reduce or avoid include, for example: drive shafts,brackets, and transmission housing. The method deactivates cylindermodes if the engine combustion frequency approaches a predeterminedmodal frequency.

Engine speed is anticipated because cylinder mode transitions take aperiod of time to initiate and because it also may take time to allow atorque converter to exit lock-up mode and begin to slip, reducingdriveline torque surges. In other words, when transitioning betweendifferent valve and/or cylinder modes, in one example, the torqueconverter is unlocked before the transition, to dampen any uncompensatedtorque disturbance.

In step 1610, engine speed is determined. Engine speed is determinedfrom engine position sensor 118. The routine then proceeds to step 1612.

In step 1612, variables for current transmission gear, CUR_GR, andtarget (future) transmission gear, TAR_GR, are evaluated to determine ifa gear shift is pending. The transmission controller determines currentand target gears from engine speed, driver brake torque demand,transmission temperature, and signals alike, for example. If CUR_GR andTAR_GR are different, a transmission shift is pending or is in progress.If a gear shift is pending or is in progress the routine proceeds tostep 1614. If a gear shift is not in progress or pending, the routineproceeds to step 1616.

In step 1614, engine speed is predicted into the future by multiplyingthe current engine speed by the ratio of current and target gear ratios.In automatic transmissions, the slip of a torque converter can also beincorporated into gear based anticipation. This allows engine combustionfrequencies that are influenced by transmission gears to be reduced oravoided.

When a transmission shifts gears, the engine speed can change quickly asthe engine speed and vehicle speed are brought together through thetransmission gear set. Engine speed is anticipated during gear shiftingby the equation:${{Ant\_ Eng}{\_ N}} = {{Eng\_ N} \cdot \frac{{Tar\_ Gr}{\_ Rto}}{{Cur\_ Gr}{\_ Rto}}}$Where Ant_Eng is the anticipated engine speed, Eng_N is the currentengine speed, Tar_Gr_Rto is the target (future) gear ratio, andCur_Gr_Rto is the current gear ratio. The equation predicts engine speedduring up and down shifting so that excitation of modal frequencies canbe avoided. The routine then proceeds to step 1618.

In step 1616, engine speed is predicted based on current and past enginespeed measurements. Engine speed is predicted by the equation:${{Ant\_ Eng}{\_ N}} = {{{Eng\_ N}(k)} + {{Ant\_ Tm} \cdot \frac{{{Eng\_ N}(k)} - {{Eng\_ N}\left( {k - 1} \right)}}{\Delta\quad t}}}$Where Ant_Eng is the anticipated engine speed, Eng_N(k) is the currentengine speed, Eng_N(k−1) is engine speed of the previous engine speedsample, Ant_Tm is the anticipation time, i.e., period of timeanticipated into the future, and Δt is the time duration betweensamples. The anticipation time, Ant_Tm, should be less than 0.5 seconds.

Alternatively, engine speed may be used in place of predicted enginespeed, but speed thresholds of each cylinder and valve mode are loweredto avoid encountering NVH areas. The routine then continues to step1618.

In step 1618, anticipated engine speed is converted into combustionfrequencies that are associated with cylinder modes. For example, ananticipated engine speed of 1500 RPM for an engine operating infour-stroke mode with eight active cylinders translates to a firingfrequency of 100 Hertz (1500 Rev/min*1 min/60 sec*4 firing/Rev).

These frequencies are then compared to a predetermined undesirablecylinder mode frequency so that excitation of modal frequencies isavoided or reduced by activating or deactivating cylinders and/orvalves. Further, the number of strokes in a cycle of a cylinder may alsobe changed to avoid undesirable frequencies. For example, if the modalfrequency of a vehicle chassis is 15 Hz it is desirable to avoid thisand lower frequencies. An engine operating at 800 RPM has a V8combustion frequency of 53.3 Hz, a V4 combustion frequency of 26.6 Hz,and a V2 combustion frequency of 13.3 Hz. Therefore, in this example, V2cylinder mode can be deactivated. Further, step 1620 provides an offsetto the predetermined desired frequency of step 1618. If the cylinderload, or cylinder air amount, is low, the predetermined desiredfrequency can be lowered as a function of the cylinder load. Typically,a cylinder load below 30% of cylinder load capacity will lower thepredetermined frequency capacity. The routine then exits.

In addition, the number of valve events during a cycle of an activecylinder may also be used to avoid frequencies (or reduce the impact)that are a result of valve operations. In other words, when a valve isoperated it generates a different frequency than the cylinder combustionfrequency because the valve operates at least twice in an activecylinder, one time opening and one time closing. These frequencies mayalso be avoided or reduced in step 1618 by identifying valve frequenciesbased on valve and cylinder modes.

Further, frequencies that affect driveline and drive shaft vibration orare affected by the state of a torque converter lock-up clutch may beavoided or reduced by simply changing combustion frequency and valveevents as described above.

Further yet, a signal may be output from step 1618 to change a dampingratio of a motor mount having variable characteristics. As cylindercombustion frequency and valve operating frequency approach apredetermined value, a signal may be sent to an external routine toalter motor mount damping ratios to further reduce any noise orvibration.

Referring to FIG. 17, a flowchart of a method to deactivate cylindermodes based on desired engine brake torque is described. The methodevaluates desired engine brake torque and predicts future engine braketorque so that torque is smoothly applied between cylinder and valvemode transitions.

In step 1710, desired engine brake torque is determined from acceleratorpedal 119. The routine then proceeds to step 1712. Note that otherengine output parameters could be used in place of engine brake torque,such as wheel torque, transmission input torque, transmission outputtorque, engine indicated torque, and others. Further, it can also bebased on engine or vehicle speed.

In step 1712, the method determines if desired brake torque isincreasing or decreasing. In one example, the current desired braketorque is subtracted from the previous sample value of desired enginebrake torque. If the sign of the result is positive, brake torque is (ordetermined to be) increasing. If the result is negative, desired braketorque is (or determined to be) decreasing. If the desired brake torqueis increasing, the method proceeds to step 1716. If the desired braketorque is decreasing the method proceeds to step 1714. Further, theroutine can also have a third option that looks to whether the torque isremaining substantially steady (e.g., not changing within 0-5%, forexample). If such a condition is detected, in this example, the routinecontinues to step 1716.

In step 1714, the desired engine brake torque signal is filtered by afirst order filter and a predetermined time constant, although higherorder filters could be used, or other types of filters could be used. Byfiltering the decreasing desired brake torque signal, potential ofincreased frequency of switching between multiple cylinder and valvemodes can be reduced. For example, if the vehicle driver depresses andthen releases the accelerator 119 multiple times over a short period,the filter can reduce the number of mode changes because the filtereddesired torque signal decays, i.e., goes to a lower value, at a slowerrate than the unfiltered desired torque signal. In an alternativeembodiment, both increasing and decreasing signals can be filtered andthen used with a dead-band to reduce the amount of unnecessary valve orcylinder mode switching in response to driver changes. The method thencontinues to step 1718.

In step 1716, the increasing desired brake torque signal is predictedinto the future by an anticipation algorithm. Desired engine torque isanticipated by the equation:${{Ant\_ Eng}{\_ Tor}} = {{{Eng\_ Tor}(k)} + {{Ant\_ Amt} \cdot \frac{{{Eng\_ Tor}(k)} - {{Eng\_ Tor}\left( {k - 1} \right)}}{\Delta\quad t}}}$Where Ant_Eng_Tor is the anticipated desired engine torque, Eng_Tor(k)is the current desired engine torque, Eng_Tor(k−1) is desired enginetorque of the previous desired engine torque sample, Ant_Amt is theanticipation time, i.e., period of time anticipated into the future, andΔt is the time duration between samples. The anticipation time, Ant_Amt,in one example, is less than 0.5 seconds.

Alternatively, desired engine torque may be used in place of predicteddesired engine torque, but torque thresholds of each cylinder and valvemode are lowered to avoid encountering the torque capacity of a mode.The routine then continues to step 1718.

In step 1718, desired engine torque is compared to a matrix,Eng_Mod_Tor, of torque capacity amounts for cylinder and valve modes.Each cell of the cylinder and valve mode matrix has a corresponding cellin the Eng_Mod_Tor matrix. If the desired engine torque is greater thanthe torque capacity of a cylinder and valve mode, then the cylinder andvalve mode is deactivated. In other words, the desired torque iscompared against the torque capacity of each cylinder and valve mode. Ifthe desired torque is greater than a cylinder and valve mode, the modeis deactivated. The routine then exits.

Referring to FIG. 18, a method to select a cylinder and valve mode froma matrix of available cylinder and valve modes is described. In oneexample, the method searches the entire mode matrix for a mode with theleast number of active cylinders and valves. Since the before-mentionedsteps have already deactivated cylinder and valve modes based onoperating conditions of the engine and vehicle, this step provides asecond example criteria for selection of cylinder and valve modes,namely, fuel economy. By selecting the fewest number of active cylindersand valves, fuel economy is increased by improving cylinder efficiencyand reducing electrical power consumption. However, alternative searchschemes can be used by structuring the columns and rows of the matrixdifferently to emphasize other goals, or combinations of differentgoals.

In step 1810, row and column indexes are initialized each time theroutine is executed and the routine stores the current row and columnindex if the mode matrix cell pointed to by the indexes contains a valueof one. In this example, only one row and column index is stored at atime. The routine proceeds to step 1812 after the current mode matrixcell is evaluated.

In step 1812, the current column number, cols, is compared to the numberof columns of the mode matrix, col_μm. If the currently indexed columnis less than the total number of mode matrix columns the routineproceeds to step 1814. If the indexed column is not less than the totalnumber of mode matrix columns the routine proceeds to step 1816.

In step 1814, the column index value is incremented. This allows theroutine to search from column zero to column col_lim of each row. Theroutine then continues to step 1810.

In step 1816, the column index is reset to zero. This action allows theroutine to evaluate every column of every row of the mode matrix ifdesired. The routine then proceeds to step 1818.

In step 1818, the current row number, rows, is compared to the number ofrows of the mode matrix, row_lim. If the currently indexed row is lessthan the total number of mode matrix rows the routine proceeds to step1820. If the indexed row is not less than the total number of modematrix rows the routine proceeds to step 1822.

In step 1820, the row index value is incremented. This allows theroutine to search from row zero to column row_lim of each row. Theroutine then continues to step 1810.

In step 1822, the routine determines the desired cylinder and valvemode. The last row and column indexes are output to the torquedetermination routine, FIG. 2, step 212. The row number corresponds tothe desired cylinder mode and the column number corresponds to thedesired valve mode. The routine then exits.

Referring to FIG. 19, a timing chart that illustrates alternating intakevalve control is shown. The x-axis is designed to show two enginerevolutions, or one cylinder firing cycle (combustion cycle) for acylinder in four-stroke mode (although other strokes can be used). Inthis example, a cylinder with two intake valves (labeled “A” and “B”) iscontrolled according to the timing diagram of FIG. 19. The position ofintake valve A opens prior to the 360 degree crankshaft marking, and itdoes not open at the next 360 degree crankshaft marking, but it opensagain at the following 360 degree crankshaft marking. In other words,the A valve opens every other combustion event, in the case where theengine is operating in a four-stroke mode, the cylinder firing every 720degrees of crankshaft rotation, or every two revolutions. The secondintake valve also opens at a 360 degree crankshaft marking too, butvalve B opens 720 degrees out of phase with valve A. Also, this valvesequence is possible for both intake and/or exhaust valves.Alternatively, some cylinders of the engine can operate with alternatingvalves while others operate with the same single valve, or dual valves.

The (full or partial) alternating valve sequence can advantageouslyreduce valve wear, reduce exhaust valve temperature, and/or reduce powerconsumption. Further, the valve sequence can alter engine breathingcharacteristics, i.e., the amount of air inducted, when different lengthintake or exhaust manifold runners are available for the differentintake and exhaust valves. The valve sequence is one of many sequencesand operating patterns available for electromagnetically actuated valvesand may be selected by the method of FIG. 10.

Referring to FIG. 20, a timing chart that illustrates an example ofintake valve phasing control is described. A cylinder with two intakevalves is controlled according to the timing diagram of FIG. 20. Intakevalve A opens prior to each 360 degree crankshaft marking. On the otherhand, valve B opens at the 360 degree crankshaft marking. The angulardifference between the valve openings is a valve phase difference, andcan be varied based on engine or vehicle operating conditions, includingvalve operating conditions. Further, the valve opening location, valvelift, and duration of each of valves A and B can also be adjusted basedon these conditions. It is also possible to open valve A before valve Bor to operate valve B before valve A based on engine speed and load, orother conditions, such as valve operating conditions. Thus, in someoperating modes, valve A opens (or closes) before valve B, and in othermodes (at other conditions, such as temperature, speed, load, catalyststorage amounts, etc.) valve B opens (or closes) before valve A.

Further, the amount of phasing can also be based on engine speed andload, or other conditions, such as valve operating conditions. Valvephasing has potential benefits for both intake and exhaust valves. Forintake valves, valve phasing can increase charge motion at idle andlower engine speeds. This increased charge motion can be combined with alean air-fuel mixture to reduce expelled engine hydrocarbons during astart, for example. Further, valve phasing can also alter intakebreathing which may improve the signal to noise ratio of sensors thatare used to estimate engine air amount, such as the manifold pressuresensor, and/or mass air flow sensor.

Exhaust valves may also be phased (e.g. opening phasing and/or closingphasing can be used, as with intake valves) to improve engine operation.For example, exhaust valve phasing offers the opportunity to reduceelectrical power consumption. By opening a single valve followed by asecond valve, as opposed to simultaneously opening two valves, during anexhaust stroke when cylinder pressures are elevated, less energy goesinto opening the second exhaust valve. Alternatively, in someconditions, simultaneous opening and/or closing can be used. Further,combination of intake and exhaust phasing can be used, at least on somecylinders, if desired.

Intake and exhaust valve phasing may also be combined with cylindergrouping, multi-stroke, and alternating valves, and combinations andsubcombinations thereof, to further enhance engine performance and fueleconomy. Valve phasing is one of many sequences available forelectromagnetically actuated valves and may be selected by the method ofFIG. 10 by including it as an available valve mode, if desired.

Referring to FIG. 21, a cylinder and valve configuration that offersflexible control options with reduced cost is shown. The M labeldesignates a mechanical valve operated by a camshaft (optionally havinghydraulically actuated variable cam timing) while the E designates anelectromechanical valve. The figure shows two cylinder groups, one groupwith electromechanically actuated intake valves and the other group withmechanically actuated intake valves. It is also possible to configuregroup two with mechanical intake valves and electromechanical exhaustvalves. Yet another configuration may be where one group of cylindershas one or more electromechanically actuated valves and the remainingvalves in the engine are mechanically activated. This allows thecylinder groups to have different valve configurations for differentobjectives. For example, one cylinder group may operate with four valveswhile the other group operates with two valves. This allows the fourvalve cylinders to have a higher torque capacity during some conditions,such as speed and load conditions, and allows the engine to havemultiple torque capacity amounts by selectively activating theelectromechanically actuated valves.

By operating two cylinder groups with different valve configurations,engine fuel economy can also be increased. For example, a V10 enginewith two cylinder banks can be configured with a mechanically actuatedvalve bank and either an electromechanically actuated or combinationmechanical/electromechanically actuated valve bank. Cylinders in theelectromechanical bank may be deactivated as desired without the cost ofinstalling electromechanical valves in all cylinders.

Further, engine emissions may be improved in an exhaust configurationwhere catalyst bricks are located at different distances from cylinderheads. A bank of cylinders with electromechanically actuated valves canretard exhaust valve timing, thereby increasing heat for the cylinderbank where the catalyst bricks are located further away from thecylinder head. Consequently, the different cylinder banks can beconfigured based on engine design to improve emissions.

Referring now to FIG. 21A, an alternative configuration is shown withelectrically actuated intake valves, and mechanically cam actuatedexhaust valves (optionally with hydraulically actuated variable camtiming). Note that while two intake and two exhaust valves are shown, inyet another alternative embodiment, one electrically actuated intake,and one cam actuated exhaust valve can be used. Further, twoelectrically actuated intake valves, and one cam actuated exhaust valvecan also be used.

Referring to FIG. 22, an alternative grouped cylinder and valveconfiguration is shown. The configuration of FIG. 22 offers some of thesame benefits as those described for FIG. 21, but all cylinders areshown with mechanical and electromechanically actuated valves. Thisconfiguration offers further control flexibility by allowing allcylinders to be mechanically controlled or by operating a mechanicalgroup and a mechanical/electromechanical group. Placing theelectromechanical valves and mechanical valves in different locations inthe different cylinder groups can further alter this embodiment. Forexample, group one could be configured with electromechanical intakevalves and mechanical exhaust valves while group two is configured withmechanical intake valves and electromechanical exhaust valves.

The cylinder and valve configurations of FIGS. 21, 21A, and 22 may befurther altered by changing electromechanical valve locations formechanical valve locations or by rearranging valve patterns. Forexample, one cylinder group arrangement may configure electromechanicalintake and exhaust valves into a diagonal configuration that promotescylinder charge swirl instead of the illustrated opposed valveconfiguration.

Referring to FIGS. 23 and 24, additional embodiments of grouped cylinderand valve configurations are shown. The valve locations designated by anS, the selected valve, are operated during a cycle of the engine. Notethat additional valves may be mechanically operated by a cam, in someexamples. The cylinder and valve configurations shown divide thecylinder into two regions (between intake and exhaust valves in FIG. 23,and between groups of intake and exhaust valves in FIG. 24). Further,additional configurations can be used where the selected valve is in thesame region but is not selected in the figure. These configurations canhave at least some of the same benefits as the configurations as thosedescribed for FIGS. 21-22, for example.

Referring to FIGS. 25, 26 and 27, yet further embodiments of groupedcylinder and valve configurations are shown. The valve locationsdesignated by an S, the selected valve, are operated during a cycle ofthe engine. The cylinder and valve configurations shown break thecylinder into four regions, each region having an electromagneticallyactuated valve, regions 1 and 2 containing intake valves, and regions 3and 4 containing exhaust valves. Further, additional configurations canbe used where the selected valve is in an alternate region but is notselected in the figure. These configurations can have the same benefitsas the configurations described for FIGS. 21-24, but the configurationscan also offer more control flexibility. For example, multi-stroke,valve phase control, alternating valves, and combinations thereof, asdescribed by FIGS. 19 and 20, can be implemented in grouped cylindercontrol. Further, the selected valve patterns can be altered to provide2, 3, and 4 valve operation.

Referring to FIG. 28, a plot of a speed dependent cylinder and valvemode change by the method of FIG. 10 is shown. The plot shows fourseparate plots of signals of interest during a speed dependent modechange. The top plot shows actual engine speed referenced to time.Engine speed starts at approximately 800 RPM and is ramped up to 1500RPM then ramped back down to 800 RPM. The third plot of requested modeverses time shows speed dependent mode hysteresis. That is, a moderequest is initiated at 1100 RPM for increasing engine speed and anothermode request is initiated at 950 RPM for decreasing engine speed. Theengine speed based cylinder and valve mode transition points forincreasing and decreasing engine speed are calibrated as desired. Thesecond plot from the top is a plot of anticipated engine speed. There isincreased variation in the engine speed signal as compared to the topplot. This variation is due to the differentiation used in theanticipation algorithm. This signal is the basis for speed dependentmode changes. Anticipated engine speed leads the actual speed duringaccelerations and decelerations, allowing mode transitions to beexecuted before the actual engine speed reaches the predeterminedcylinder and valve mode transition speed. The third and fourth plotsfrom the top show the requested mode and the target mode. The requestedmode leads the target mode. This lead time allows the transmissiontorque converter to begin slipping so that the torque disturbance of acylinder and valve mode change is dampened in the vehicle driveline.

Referring to FIG. 29, a plot shows engine torque capacity of a V8 engineoperating in a variety of cylinder modes. The torque modes shownillustrate the different torque capacity of an engine as cylinders aredeactivated and the number of cylinder strokes is increased. Further,additional torque capacities could be shown for specific valve modes.For example, two valve V8 operation would have a different torquecapacity curve than four valve V8 operation. In one example, a strategyof mode transition is employed where a transition between modes isperformed before the torque capacity of a given cylinder and valve modeis reached. By doing this, the driver can experience a more continuoustorque progression through the various available modes.

Referring to FIG. 30, a plot of a torque dependent cylinder and valvemode change by the method of FIG. 10 is shown. The Figure shows fourseparate plots of signals of interest during a torque dependent modechange. The top plot shows actual desired engine torque referenced totime. Engine torque starts at approximately 100 N-M and is ramped up to200 N-M then ramped back down to 100 N-M. The third plot of requestedmode verses time shows engine torque dependent mode hysteresis andfiltering of desired torque. That is, a mode request is initiated at 130N-M for increasing desired engine torque and another mode request isinitiated at 110 N-M for decreasing desired engine torque that is alsodelayed in time. The engine torque cylinder and valve mode transitionpoints for increasing and decreasing desired engine torque arecalibrated as desired. The second plot from the top is a plot ofanticipated and filtered desired engine torque (anticipated torque whendesired torque increases and filtered torque when desired engine torquedecreases). Notice, anticipated and filtered torque leads desired torquefor increasing desired engine torque and lags, due to filtering,decreasing engine torque. The third and fourth plots from the top showthe requested mode and the target mode. Notice, that the requested modeleads the target mode. Also, the requested mode transition duringdecreasing desired torque occurs long the after desired engine torquereaches 100 N-M. This lead time allows the transmission torque converterto begin slipping so that the torque disturbance of a cylinder and valvemode change is dampened in the vehicle driveline. The calibration of thefilter time constant and the torque hysteresis allows the modetransition logic to avoid multiple mode transitions if the driverrapidly cycles the accelerator pedal 119.

Referring to FIG. 31, a plot of independent speed and torque basedcylinder and valve mode changes initiated by the method of FIG. 10 isshown. The top plot shows anticipated engine speed while the second plotshows anticipated and filtered desired engine torque. The third plotfrom the top shows the actual desired mode change request. The firstmode transition, labeled #1, is based on anticipated engine speed alone.The second, third, fourth, and fifth transitions are based onanticipated engine speed and desired anticipated filtered engine torque.The competing engine speed and torque requests are thus able to behandled by the mode selection approach.

While electromechanically actuated valves present various opportunitiesto increase fuel economy and engine performance, they can also improveengine starting, stopping, and emissions in other ways. FIG. 32illustrates a method to improve engine starting by controlling intakeand exhaust valves.

As one example, electromechanically actuated valves allow the ability toselect the first cylinder to carry out combustion during a start. In oneexample, at least during some operating conditions, a consistentcylinder is selected for performing the first combustion, which canprovide reduced emissions. In other words, when an engine is started onthe same cylinder, at least during two subsequent starts under selectedconditions, variation in the amount of fuel delivered into each cylinderduring a start can be decreased. By beginning fuel injection in the samecylinder, unique fuel amounts can be repeatedly delivered into eachcylinder. This is possible because fuel may be scheduled from the samereference point, i.e., the first cylinder selected to combust anair-fuel mixture. In general, because of packaging constraints, no twocylinders have identical intake ports in a multi cylinder engine.Consequently, each cylinder has a unique fuel requirement to produce adesired in cylinder air-fuel mixture. Fortunately, one example of themethod described herein allows fuel injected into each individualcylinder to be tailored to each unique port geometry, port surfacefinish, and injector spray impact location, thereby, reducing air-fuelvariation and engine emissions.

In another example, to reduce wear caused by repeatedly carrying out afirst combustion, the cylinder selected for repeatedly carrying out thefirst combustion is varied. It can be varied based on various sets ofoperating conditions, such as a fixed number of starts, enginetemperature, a combination thereof, or others. Thus, for a first numberof starts, cylinder 1 is repeatedly used to start the engine. Then, fora second number of starts, another cylinder (e.g. a first availablecylinder, or the same cylinder such as cylinder number 2) is repeatedlyused to start the engine. Alternative, a different cylinder is selectedbased on engine or air temperature. In still another example, differentcylinders for starting are selected based on barometric pressure(measured or estimated, or correlated to other parameters that aremeasured or estimated).

Referring to FIG. 32, in step 3210, the routine determines if a requestto start the engine has been made. A request may be made by an ignitionswitch, a remotely transmitted signal, or by another subsystem, e.g., avoltage controller of a hybrid power system. If not, the routine exits.If so, the routine proceeds to step 3212.

In step 3212, all exhaust valves are closed. The valves may besimultaneously closed or may be closed in another order to reduce powersupply current. Also, in an alternative embodiment, less than all of theexhaust valves can be closed. The closed valves remain closed until acombustion event has occurred in the respective cylinder of the valves.That is, the exhaust valve for a cylinder remains closed until a firstcombustion event has occurred in the cylinder. By closing the exhaustvalve, residual hydrocarbons can be prevented from exiting the cylinderduring engine cranking and run-up (a period between cranking and beforeachieving a substantially stable idle speed). This can reduce emittedhydrocarbons and thereby can reduce vehicle emissions. The routine thenproceeds to step 3214.

In addition, intake valves may be set to a predetermined position, openor closed. Closing intake valves during cranking increases pumping workand starter motor current, but can trap hydrocarbons in a cylinder.Opening intake valves during cranking decreases pumping work and startermotor current, but may push hydrocarbons into the intake manifold. Assuch, various combinations of open and closed intake valves can be usedfor example. In another example, closed intake valves are used. And, instill another example, open intake valves are used. The descriptions ofFIGS. 49-53 provide detailed explanations of additional valve sequencingembodiments that may be used to start an engine by the method of FIG.32.

Alternatively, all exhaust valves may be set to an open position and theintake valves set to a closed position until engine position isestablished. Then exhaust valves in respective cylinders are closed atbottom-dead-center of piston travel and intake valves are operated basedon a desired combustion order. The exhaust valves are operated after afirst combustion event in the respective cylinders based on the desiredengine cycle. Hydrocarbons are pumped out of a cylinder and then drawnback into the cylinder, being combusted in a subsequent cylinder cycleby this method. This can reduce emitted hydrocarbons when compared tomechanical four-stroke valve timing.

In step 3214, the engine is rotated and engine position is determined byevaluating the engine position sensor 118. A sensor that can quicklyidentify engine position can be used to reduce engine crank time and istherefore preferred. The routine then proceeds to step 3216.

In step 3216, engine indicated torque, spark advance and fuel aredetermined by the method of FIG. 10. The engine is started using apredefined desired engine brake torque, engine speed, spark advance, andLambda. Lambda is defined as follows:${{Lambda}(\lambda)} = \frac{\frac{Air}{Fuel}}{\frac{Air}{{Fuel}_{stoichiometry}}}$This is in contrast to conventional engines that are started by matchingthe fuel to an engine air amount estimate that is based on fixed valvetiming. The method of FIG. 10 adjusts valve timing and spark angle toproduce the desired torque and engine air amount. By adjusting the valvetiming and/or lift to meet torque and air amount requirements duringcranking and/or starting, the engine can be made to uniformly accelerateup to idle speed, start after start, whether at sea level or altitude.FIGS. 35 and 36 show example valve timing for producing uniform sealevel and altitude engine starts.

Further, the method of FIG. 32 can reduce variation in the mass of airand fuel required to start an engine. Nearly the same torque can beproduced (if desired) at altitude and sea level by adjusting valvetiming, injecting an equal amount of fuel, and similar spark timing.Only small adjustments for altitude are made to compensate for fuelvolatility and engine back pressure differences. The method continues onto step 3218.

Providing uniform engine starting speeds can also be extended to enginestrategies that are not based on engine torque. For example, apredetermined target engine air amount may be scheduled based on anumber of fueled cylinder events and/or engine operating conditions(e.g., engine temperature, ambient air temperature, desired torqueamount, and barometric pressure). The method of step 222 uses the idealgas law and cylinder volume at intake valve closing timing to determinethe valve timing and duration. Next, fuel is injected based on thetarget engine air amount and is then combusted with the inducted airamount. Because the target engine air amount is uniform or nearlyuniform between sea level and altitude, valve timing adjustments aremade while the fuel amount remains nearly the same (e.g. within 10%). Inanother example, a target fuel amount based on the number of fueledcylinder events and/or engine operating conditions (e.g., enginetemperature, ambient air temperature, catalyst temperature, or intakevalve temperature) may also be used to start an engine. In this example,a cylinder air amount based on the target cylinder fuel amount isinducted by adjusting valve timing to achieve the desired air-fuelratio. The desired air-fuel ratio (e.g., rich, lean, or stoichiometric)is then combusted to start the engine. In addition, spark advance may beadjusted based on the cylinder air amount, valve timing may be furtheradjusted based on ambient air temperature and pressure, and fuel may bedirectly injected or port injected using this starting method.

Note that while it may be desirable to provide uniform engine startingspeeds under various conditions, there may be conditions in which otherapproaches are used. Further, it may be desired to provide a desired airamount during a start based on an operating condition of an engine byadjusting valve timing based on engine position and desired cylinder airamount, or a desired torque, etc., even if a consistent engine speedtrajectory is not used.

In step 3218, the routine determines if combustion will be initiated ina predefined cylinder or in a cylinder that can complete a first intakestroke (e.g. a first available cylinder for combustion). If combustionis selected in a predefined cylinder the cylinder number is selectedfrom a table or function that may be indexed by an engine operatingcondition or engine characteristic.

By selecting a cylinder to begin combustion, and by selecting the firstcombusting cylinder based on engine operating conditions, (start afterstart if desired) engine emissions can be improved. In one example, if afour-cylinder engine is started at 20° Celsius, cylinder number one maybe selected to produce a first combustion event each time the engine isstarted at 20° Celsius. However, if the same engine is started at 40°Celsius, a different cylinder may be selected to produce a firstcombustion event, this cylinder may be selected each time the engine isstarted at 40° Celsius, or alternatively, a different cylinder may beselected depending on engine control objectives. Selecting a startingcylinder based on this strategy can reduce engine emissions.Specifically, fuel puddles are commonly created in intake ports of portfuel injection engines. The injected fuel can attach to the intakemanifold walls after injection and the amount of fuel inducted can beinfluenced by intake manifold geometry, temperature, and fuel injectorlocation. Since each cylinder can have a unique port geometry andinjector location, different puddle masses can develop in differentcylinders of the same engine. Further, fuel puddle mass and enginebreathing characteristics may change between cylinders based on engineoperating conditions. For example, cylinder number one of afour-cylinder engine may have a consistent fuel puddle at 20° Celsius,but the puddle mass of cylinder number four may be more consistent at40° Celsius. This can occur because the fuel puddle may be affected byengine cooling passage locations (engine temperature), ambient airtemperature, barometric pressure, and/or a characteristic of the engine(e.g., manifold geometry and injector location).

Also, the location and temperature of a catalyst may also be used todetermine a first cylinder to combust. By considering the location andtemperature of a catalyst during a start engine emissions can bereduced. For example, in an eight cylinder, two bank engine, it may bebeneficial to produce a first combustion event in cylinder number four(bank one) for one of the above-mentioned reasons. On the other hand,after the engine is warm, it may be beneficial to start the same engineon cylinder number five (bank two) if the catalyst in bank two islocated closer to cylinder number five, compared to the catalyst in bankone, relative to cylinder number four. The closer and possibly warmercatalyst in bank two may convert hydrocarbons, produced during a highertemperature start, more efficiently, compared to the catalyst in bankone.

In addition, engine hardware characteristics may also influenceselection of a first cylinder to combust. For example, cylinder locationrelative to a motor mount, and/or oxygen sensor location may be factorsat one set of engine operating conditions and may not be used as factorsat a different set of engine operating conditions. This strategy may beused if a cylinder selected for a first combustion event reduces enginenoise and vibration at a lower temperature, but another cylinder hasimproved characteristics at a different temperature.

Also, the amount of lost fuel, fuel that is injected into a cold enginebut not observed in exhaust gases due to fuel puddles and migration intothe crankcase, can change each time a cylinder combusts due to cylinderring expansion. Further, the amount of lost fuel in a specific cylindermay change depending on the engine operating conditions. Therefore, itcan be beneficial to select one cylinder for a first combustion eventbased on one set of engine operating conditions, and to select adifferent cylinder for a first combustion event based on a second set ofoperating conditions. Then, individual fuel amounts can be delivered toindividual cylinders, in the same order, starting with the firstcylinder to combust, such that fuel amount variability may be reduced.Thus, the same fuel amount can be injected into the same cylinder thathas nearly the same (such as within 1%, within 5%, or within 10%) puddlemass, start after start.

Thus, it may be beneficial to select and/or change a first cylinder tocombust, during a start, based on engine operating conditions and/orengine characteristics.

Note that combustion can also be started in multiple cylinders, ifdesired.

Also, in an engine of “I” configuration, i.e., I4 or I6, selecting apredetermined cylinder located closest to the flywheel or near thecenter of the engine block can reduce torsional vibration created bycrankshaft twist during a start, at least under some conditions.Crankshaft twist is a momentary angular offset between the crankshaftends that may occur during a start due to engine acceleration.Generally, the first cylinder to fire inducts a high air charge in aneffort to accelerate the engine from crank to run speed, therebyproducing a large acceleration. If an engine is started on a cylinderthat is furthest from the location of the engine load, i.e., theflywheel, the crankshaft may twist due to the force exerted on thecrankshaft by the piston and the distance from the combusting cylinderto the load. Therefore, selecting a predetermined cylinder that islocated closest to the engine load or that has more support, i.e., alocation central to the engine block, can reduce engine vibration duringa start. And, by selecting a cylinder to start an engine on that reducesvibration, customer satisfaction may be improved.

However, selecting a predetermined cylinder closest to the flywheel inwhich to carry out a first combustion event may increase engine cranktime given a conventional mechanically constrained valve train.Nevertheless, an engine with electromechanical valves is notmechanically constrained. Rather, engine valve timing can be adjusted tocreate an intake stroke on the first cylinder, closest to the engineflywheel, where the piston is capable of producing a vacuum in thecylinder. For example, this can be the cylinder closest to the flywheelwith a downward moving piston where sufficient vacuum is created to pullthe injected fuel into the cylinder, enabling an engine output to beproduced. Subsequent combustion can then proceed based on conventionalfour-stroke valve timing.

Thus, in one example, after processing a signal indicative of an enginestart (or engine position), the routine sets an intake stroke on thefirst cylinder with sufficient piston downward movement to produce anengine output (e.g., engine torque, or a desired cylinder charge). Oncethis is set, the remaining cylinders can have their respective valvetimings positioned relative to the set intake stroke of said cylinder.Then, the first combustion can be carried out in the first cylinder withsufficient piston downward movement, and subsequent combustion can becarried out in the remaining cylinder based on the position valvetimings in the selected firing order.

Returning to FIG. 32, if combustion is desired in a predefined cylinderthe routine proceeds to step 3222. If combustion in a predefinedcylinder is not desired the routine proceeds to step 3220.

In step 3220, the routine determines which cylinder can capture or trapthe desired cylinder air amount first. The position of a piston and itsdirection of motion, up (traveling toward the cylinder head) or down(traveling away from the cylinder head) can also factor into thisdetermination, as indicated below in the description of FIG. 54. Byselecting a cylinder that is capable of first capturing the desiredcylinder air amount, starting time can be reduced. Alternatively,selecting a cylinder capable of a first combustion event may also reduceengine starting time. However, engine starting speed and emissionsvariability can be affected. The type of fuel injection can also affectthe cylinder selection process. Port fueled engines rely on an intakestroke to induct fuel and air into a cylinder. However, late intakevalve closing is also possible but inducting the desired cylinder fuelamount can be more difficult. Therefore, selecting a cylinder for afirst combustion event, for a port injected engine, can be defined by acapacity of a cylinder to induct both air and fuel.

On the other hand, direct injection engines inject fuel directly intothe cylinder providing an opportunity to combust fuel with air that istrapped by closing the intake and exhaust valves. Given a sufficienttrapped volume of air, an intake cycle of the valves may not benecessary to facilitate combustion in a cylinder because air trapped inthe cylinder can be mixed with fuel that is directly injected into thecylinder. Therefore, engine valve timing can be adjusted based on engineposition to facilitate combustion in the first cylinder, nearest theflywheel, capable of capturing and compressing a desired air amount.

In addition, engines commonly have two pistons that are in the samecylinder position, relative to one another. Combustion in the cylinderscan be defined by selecting the appropriate valve timing for therespective cylinders. Since electromechanical valves can be operatedwithout regard to crankshaft position, an engine control strategy canselect which of the two cylinders will combust first by applying theappropriate valve timing. Therefore, in step 3220, the strategy selectsa cylinder based on its ability to capture a desired cylinder air amountand then sets the appropriate valve timing between competing cylinders.For example, a four-cylinder engine with pistons in cylinders 1 and 4 inposition to complete a first induction stroke, cylinder 1 is selected toproduce a first combustion event. In addition, example criteria toselect one of two cylinders competing for a first combustion eventinclude cylinder position, starting noise and vibration, and cylinderair-fuel maldistribution. For example, in a four-cylinder engine,cylinder number four is located closest to the engine flywheel. Thecrankshaft may experience less twist during a start if cylinder fourfires before cylinder one. This may reduce engine noise and vibrationduring a start. In another example, a certain cylinder may be locatedcloser to engine mounts. The proximity of a cylinder to engine mountsmay also influence which cylinder to select for a first combustionevent. In yet another example, manufacturing processes and/or designlimitations may affect air-fuel distribution in cylinders of an engine.Selecting a cylinder based on engine characteristics may improveair-fuel control during a start. The routine continues on to step 3222.

In step 3222, fuel is injected based on engine position and desiredtorque, spark, and Lambda from step 3216 above. In the method of FIG.32, fuel can be injected on open or closed valves, delivered to allcylinders at the same time, or be delivered to individual cylinders inindividual amounts. However, in one example, fuel is preferentiallyinjected on an individual cylinder basis so that the fuel amount can betailored to a cylinder event. The period of the cylinder event signal isthe crank angle duration wherein a cycle of a cylinder repeats, in thecase of a four-stroke cylinder cycle a cylinder event in degrees is:720/number of engine cylinders.

In one example, fuel is injected based on the number of fueled cylinderevents and controlled individual cylinder air amounts are used toimprove engine air-fuel control. By controlling individual cylinderevent air amounts and counting the number of fueled cylinder events,then delivering the amount of fuel based on the number of fueledcylinder events counted and cylinder event air amounts, engine startingcan be improved. In other words, since engine air amount can becontrolled during a start and since the amount of fuel to achieve adesired air-fuel ratio changes based on the number of fueled cylinderevents, fuel delivery based on the number of cylinder events andindividual cylinder air amounts can improve engine air-fuel control.Consequently, fueling based on fueled cylinder events and controllingindividual cylinder air amounts can be used to lower engine emissionsand to provide uniform engine run-up speed during starting.

Furthermore, engine fuel requirements can be a function of the number offueled cylinder events rather than solely based on time. Cylinder eventscan be associated with mechanical dimensions; time is a continuum, whichlacks spatial dimensions and linkage to the physical engine. Therefore,engine fueling based on the number of fueled cylinder events can reducethe fuel variation associated with time based fueling.

Typically, the amount of fuel injected in step 3222 produces a leanmixture during cold starts. This can reduce hydrocarbons and catalystlight off time. However, the amount of fuel injected may also produce astoichiometric or rich mixture. The routine proceeds to step 3224.

In step 3224, the valves are operated starting with setting the stroke(intake) of the cylinder selected to produce a first combustion event.Alternately, another stroke (exhaust, power, compression) may be set inthe first cylinder selected to combust. Depending on the valve trainconfiguration (e.g., full electromechanical or amechanical/electromechanical hybrid), and the control objectives (e.g.,reduced emissions or reduced pumping work, etc.), valves are sequencedbased on a predetermined order of combustion, see FIGS. 33-34 and 49-53for example. Typically, during starting, all cylinders are operated in afour-stroke mode to reduce engine emissions and catalyst light off time.However, multi-stroke or a fraction of the total cylinders may also beused during starting. The routine proceeds to exit.

FIGS. 33 a and 33 b are plots that show representative intake andexhaust valve timing at a relatively constant desired torque, spark, andLambda for a four-cylinder engine operated in four-stroke mode by themethod of FIG. 32. Valve opening and closing positions are identified bya legend on the left side of the valve sequences, O for open and C forclosed.

At key on, or at an operator generated signal indicative of a request tostart the engine, electromechanically controlled intake and exhaustvalves are set to a closed position from the deactivated mid position.Alternatively, intake valves may also be set to an open position inrespective cylinders until the onset of a first intake event to reducecranking torque and starter current. In this illustration, cylinder 1 isthe cylinder selected for a first combustion event, but cylinder 3 or 2may be selected if a quicker start is desired. Once the first cylinderfor combustion is selected and the first induction event occurs, theremaining cylinders follow with four-cylinder, four-stroke, engine valvetiming, i.e., 1-3-4-2.

In the sequence, exhaust valves are set to a closed position and remainin a closed position until a combustion event has occurred in therespective cylinder. The exhaust valves begin operation at the shownexhaust valve timing thereafter. By closing exhaust valves untilcombustion has occurred in a cylinder, hydrocarbons from engine oil andresidual fuel are captured in the cylinder and combusted in the firstcombustion event. In this way, the amount of raw hydrocarbons expelledinto the exhaust system can be reduced. Further, the combustedhydrocarbons can provide additional energy to start the engine and warma catalyst.

In addition, cylinders with mechanical valve deactivators may deactivateexhaust or intake valves in a similar manner to produce similar results.

FIGS. 34 a and 34 b, are plots that show representative intake valvetiming for two engine starts, at different engine positions, of afour-cylinder engine by the method of FIG. 32. Cylinder 1 is selected asthe starting cylinder and the engine is started at a substantiallyconstant desired torque, spark, and Lambda (although in alternativeexamples, these can be variable). Valve opening and closing positionsare identified by a legend on the left side of the valve sequences, Ofor open and C for closed.

At key on, intake and exhaust valves are set to a closed position fromthe deactivated mid position. Alternatively, intake valves may also beset to an open position in respective cylinders until the onset of afirst intake event to reduce cranking torque and starter current. Fromtop to bottom, the first four valve timing events are for start #1, thesecond four valve timing events are for start #2, cylinder position isshown for start #1, and cylinder position is shown for start #2.

The figure shows an engine stop position for start #1 that isapproximately 50 degrees after top dead center of cylinders 1 and 4.Also, the plot of cylinder 1 shows from piston position that the pistonis already partially through its downward stroke motion. Key on occursat this point, and fuel could be injected at this point on an open valveso that the mixture would then be compressed and combusted as the pistontravels up in the following stroke. However, engine cranking speed atthis point may be low because of engine inertia and friction which maylead to poor fuel atomization and combustion. Therefore, the enginecontroller, in this example, waits to open the intake valve until anentire intake stroke of cylinder 1 can be completed, roughly 280 enginecrank angle degrees. The remaining cylinder valve events follow cylinder1 in the combustion order illustrated.

On the other hand, the first valve event of start #2 is approximately180 degrees after key on. The valve event occurs earlier because theengine stop position permits a full intake stroke in cylinder #1 earlierthan the engine stop position of start #1.

Start #2 also shows how to align valve timing for a strategy thatselects a cylinder for a first combustion event based on a cylinder thatcan complete a first full induction stroke. Cylinders 1 and 4 are thefirst cylinders capable of a full intake stroke because of the enginestop position. Pistons 2 and 3 are 180 degrees out of phase with pistons1 and 4 and are therefore partially through a downward stroke in theengine stop position.

Valve timing can be adjusted for direct injection (DI) engines using thesame principles. For example, fuel is injected into a cylinder of a DIengine. Further, a cylinder that is selected for a first combustionevent could also be based on piston position and direction of movement.Then the intake valve timing of the first cylinder can be adjusted toachieve a desired torque. However, fuel injection is not constrained ina DI by valve timing. Therefore, the desired engine air amount may beobtained by adjusting valve timing to open the intake valve before orafter bottom dead center of an intake stroke.

FIGS. 35 a and 35 b are plots of representative intake valve timingduring an engine start at sea level and a plot that shows representativeintake valve timing during an engine start at altitude by the method ofFIG. 32. For simplicity of explanation, both starts begin at the sameengine starting position and represent valve timing that follows adesired torque request that is used for both altitude and sea level.Substantially the same torque request is scheduled for altitude and sealevel so that the fuel delivery remains nearly constant between altitudeand sea level. However, as noted above, different torque requests couldalso be used, if desired.

In contrast, a conventional engine adjusts the amount of fuel deliveredbased on an engine air amount, which differs between sea level andaltitude due to variations in barometric pressure. This may result indifferent starting torque between sea level and altitude starts,resulting in different starting speeds between altitude and sea level.The change in engine speed and in the amount of fuel injected can thenlead to air-fuel and emissions differences between sea level andaltitude.

By adjusting valve timing as shown in FIG. 35 so that engine torque andair amount is nearly the same between altitude and sea level (e.g.,within 1%, 5%, or 10%), variation of air-fuel ratio and engine emissionsbetween altitude and sea level are reduced. And while previous hydraulicVCT systems were able to adjust valve timing, these actuators typicallywere not functional during a start (since there was little to nohydraulic pressure available). Thus by using electric valves, improvedstarting can be obtained.

The engine start #1 of FIG. 35 a is at sea level and begins with alonger valve event so that the engine will accelerate quickly fromcrank. The subsequent valve events are shorter as engine frictiondecreases and less torque is necessary to bring the engine up to idlespeed. After the first four events, the valve duration remainssubstantially constant reflecting a substantially constant torque demand(although if torque demand changed, the durations could change, forexample). Also, in one alternative, the valve opening durations canbegin to decrease after the first event. Alternatively, decreasing valveduration may be carried out over a fewer or greater number of cylinderevents. Further, the engine desired torque might change due to coldstart spark retard or from combusting lean air-fuel mixtures.

The engine start #2 is at altitude and begins with a longer valve event,when compared to the sea level valve event, so that the engine willaccelerate at approximately the same rate from crank. The subsequentvalve events are longer than the corresponding sea level valve events,but shorter than the initial valve event for the above-mentionedreasons.

Referring to FIG. 36, a plot representative of cylinder #1 valve eventsat altitude and sea level along with representative desired torquerequest and engine speed trajectories is shown. The plot shows exampleengine starting differences between starting at sea level and altitude,while obtaining a uniform engine speed with little over-shoot thatremains steady after idle speed is reached. Maintaining these enginespeed and torque trajectories between altitude and sea level can reduceair-fuel variability and emissions. Further, the driver experiences moreconsistent engine performance during a start, and therefore customersatisfaction can be improved.

Also, valve timing can be adjusted for direct injection (DI) enginesusing the same principles. For example, fuel can be injected into acylinder of a DI engine based on piston position and direction ofmovement, after valve timing has been adjusted to achieve a desiredtorque at the present altitude.

Referring to FIG. 37, a flowchart of a method to control valve timingafter a request to stop an engine or to deactivate a cylinder is shown.

In step 3710, the routine determines if a request has been made to stopthe engine or deactivate one or more cylinders. The request may beinitiated by the driver of the vehicle or from within the vehiclecontrol architecture, such as a hybrid-electric vehicle. If a request ispresent the routine proceeds to step 3712. If no request is present theroutine proceeds to exit.

In step 3712, fuel is deactivated to individual cylinders based on thecombustion order of the engine. That is, fuel injections that are inprogress complete injection, and then fuel is deactivated. Further,calculations that determine the cylinder port fuel puddle mass continueand the intake valve duration is adjusted in step 3714 to produce thedesired air-fuel ratio. Fuel puddle mass is determined with the methodin accordance with U.S. Pat. No. 5,746,183 and is hereby fullyincorporated by reference. The fuel mass after the last injection isdetermined from:${m_{p}(k)} = {\frac{\tau}{\tau + T} \cdot {m_{p}\left( {k - 1} \right)}}$Where m_(p) is the mass of the fuel puddle, k is the cylinder eventnumber, τ is a time constant, and T is sampling time. Subsequent fuelpuddle mass is obtained from:${\Delta\quad m_{p}} = {{{m_{p}(k)} - {m_{p}\left( {k - 1} \right)}} = {{m_{p}\left( {k - 1} \right)} \cdot \left( \frac{- T}{\tau + T} \right)}}$Where Δm_(p) is the fuel puddle mass entering a cylinder. Alternatively,a predefined puddle mass or a puddle mass determined from a look-uptable can be substituted for the puddle mass entering a cylinder.

In addition, spark may be adjusted in this step based on the request tostop the engine. Preferably, spark is adjusted to a value retarded fromMBT to reduce engine hydrocarbons and increase exhaust heat. Forexample, adjusting spark during shut-down, catalyst temperature may beincreased so that if the engine is restarted sometime soon, highercatalyst conversion efficiency may be achieved, due to a higher catalysttemperature. In another example, retarding spark during engine shut-downmay reduce evaporative emissions. Since hydrocarbon concentrations inexhaust gas may be reduced, exhaust gases that escape to the atmosphereduring an engine stop may have fewer hydrocarbons.

Thus, in some examples, during an engine shut-down operation, computerreadable code can be used to retard ignition timing on at least one of agroup of final combustion events during the shut-down to increaseexhaust temperature thereby improving emissions on a subsequent enginere-start. In one example, upon receiving a command to shut-down theengine, one or several combustion events are still carried out, e.g., 1,2, 3, 4, or a range of combustion events depending on operatingconditions, e.g., 1-5, 1-3, 1-2, etc. By adjusting the ignition timingof at least some of these (e.g., the last one, the last two, one of thelast two or three), it is possible to improve later re-starts that areperformed before the catalyst has cooled. Further, as noted above,adjusting of exhaust (or intake) valve opening and/or closing timing (orlift) can also be used (or alternatively used) to further increaseexhaust gas heat to the catalyst during a shut-down.

In step 3714, valve timing is adjusted. Upon indication of a request tostop or cylinder deactivation, intake and exhaust valve timing can beadjusted. The intake valve opening (IVO) is moved to the engine positionwhere a high intake port velocity is obtained, typically 45 degreesafter the intake stroke begins. Moving the valve opening position tothis location draws more fuel into the cylinder from the intake portpuddle for a last combustion event. This can reduce the fuel puddle whenthe cylinder is deactivated or when the engine is stopped. Furthermore,a smaller fuel puddle contributes less fuel to a cylinder when theengine is restarted, thereby leading to more accurate air-fuel controlduring a start. The routine proceeds to step 3716.

In step 3716, fuel mass and valve opening location are then substitutedinto the method of FIG. 2 which then determines valve opening durationand spark.

The valves are operated with adjusted timing for at least an intakeevent, but may be operated longer if desired. Furthermore, the intakevalve opening is typically adjusted to a location of between 30 and 180crank angle degrees after top-dead-center of the intake stroke. Theintake valve closing timing can also be adjusted to compensate aircharge differences that may result from adjusting intake valve openingtiming.

The cylinder air-fuel mixture during engine shut-down may be lean, rich,or stoichiometric depending on control objectives.

In addition, the exhaust valves and spark advance may also be adjustedduring engine shut-down. For example, exhaust valves are adjusted to anopening location of between 0 and 120 crank angle degrees aftertop-dead-center of the exhaust stroke. When this exhaust valve timing iscombined with a spark angle adjustment, additional heat can be added tothe catalyst prior to engine shut-down. As mentioned above, this canincrease catalyst temperature in anticipation of a subsequent start.Further the exhaust valve closing timing can also be adjusted based onthe adjusted exhaust valve opening time. The routine then exits.

Referring to FIG. 38, an example of a representative intake valve timingsequence during a stop of a four-cylinder engine is shown. The valvesequences begin on the left-hand side of the figure where the valvecrank angle degrees are marked relative to top-dead-center of thecombustion stroke of respective cylinders. The intake valves open at theend of the exhaust stroke indicating internal EGR flow into thecylinder. At an indication of a shut down request, the vertical line,intake valve timing is adjusted for the first cylinder where fuelinjection is deactivated after the shut down request, cylinder 1 in thisexample. Both the valve opening and valve duration are adjusted. Thevalve duration adjustment is based on an estimated fuel puddle fractionthat enters the cylinder. The valve duration adjustment provides thedesired exhaust air-fuel ratio. Alternatively, valve opening locationcan be adjusted along with scheduling a stoichiometric or lean finalinjection before deactivating fuel injection. Further, before fuelinjection is deactivated, a specific number of injections can bescheduled coincident with the valve opening position adjustment.

The figure illustrates three induction events after the valve timingadjustment is made. However, fewer or additional combustion or evennon-combustion cylinder events after each intake event can be used.

Referring to FIG. 39, a method of restarting electromechanical valves inan internal combustion engine is shown. In some cases, electromechanicalvalve actuators contain mechanical springs and electrical coils that actas electromagnets, both of which are used to regulate valve position.However, during cylinder operation pressure in a cylinder may work foror against valve operation. For example, exhaust valves overcomecylinder pressure to open, but are assisted by cylinder pressure whenclosing. As a result, capturing current, current necessary to overcomespring force, and holding current, current that holds a valve open orclosed, varies with operating conditions of the engine. The methoddescribed herein can restart a valve in and internal combustion engineif a predetermined current does not overcome an opening or closingspring force, permitting the valve to open or close during a cycle ofthe cylinder. In an inactive state (no applied voltage or current), themechanical springs position valves in a mid position that is partiallyopen. The valves can also assume the mid position if conditions in anengine do not permit the predetermined current to open or close thevalve, i.e., the valve trajectory (position) deviates from a desiredpath. If the path of a valve deviates from the desired valve trajectory,one or more attempts may be made to restart the valve so that it canresume the desired trajectory. One approach is described below.

Valve trajectory may be determined directly from sensor measurements,sensor 50 for example, or by inference from crankshaft position.

Specifically, the following method can be applied to eachelectromechanical valve in an engine to provide for valve restarting.Thus, the variables of FIG. 39 are arrays that contain data for each ofthe respective valves, although it can be applied to a subset of valves,or a single valve, if desired.

In step 3910, valve trajectory is read from valve position sensor 51 andis evaluated to determine if an error in valve trajectory has occurred.Valve position sensor 51 may be a discrete or continuous positionsensor. Desired valve position and current are determined byinterrogating four matrices that contain look-up pointers for desiredvalve trajectories and associated currents. Matrices FNVLVCURO andFNVLVCURC hold numerical pointers that identify valve current vectorsfor valve opening and closing respectively. Matrices FNVLVPOSO andFNVLVPOSC hold numerical pointers that identify valve position for valveopening and closing respectively. Both the position and current matricesare indexed by engine speed and load. The pointers contained within thematrices then determine a specific vector that contains position orcurrent information based on the valve position regions designated inFIG. 40, CL_pos_set and CL_cur_set respectively. A separate valvecontrol method accesses CL_cur_set to actuate the electromechanicalvalves. If an error in valve trajectory is determined the routineproceeds to step 3912. If no trajectory error is determined the routineproceeds to step 3932.

In step 3912, predetermined current is applied to close theoff-trajectory valve. The applied current is an upper current limitbased on the valve and power supply. Alternatively, the valve may bemoved to an open or mid position. In addition, a variable thatrepresents the number of on-trajectory valve openings and closings,Vlv_cnt, is zeroed. Further, fuel injection into the cylinder housingthe off-trajectory valve may be disabled until the valve has completed apredetermined number of on-trajectory operations. The method proceeds tostep 3914.

In step 3914, the routine determines if the off-trajectory valve hasclosed. If the valve has closed, the routine proceeds to step 3916. Ifthe valve has not closed the routine proceeds to step 3930.

Alternatively, steps 3912 and 3914 can be eliminated. In this case, if avalve is off-trajectory, valve current will be increased in the regionwhere the trajectory error was detected. The valve will stay in a midposition until a command to open or close the valve is given based onthe base valve timing. In other words, the current that drives theoff-trajectory valve is increased in the region of the detectedtrajectory error, but the valve is restarted by the base valve timing,e.g., the valve timing based on desired torque and engine operatingconditions.

In step 3930, deactivation of the off-trajectory valve and of thecylinder containing the valve occurs. The cylinder and valve aredeactivated by the cylinder and valve mode selection method of FIG. 10.The cylinder number containing the degraded valve is loaded intovariable CYL_DEG during step 3930 and is passed to step 1528 of FIG. 15.The routine then exits.

In step 3916, valve current, CL_cur, is compared against a predeterminedvariable, cur_lim. Each region of the valve trajectory profile, asillustrated in FIG. 40, begins at a predefined current level. If a valvetrajectory error occurs, valve current in all the regions of an opening(R1-R4) or closing (R4-R7) valve event is increased, steps 3930 and3922.

In addition, valve operation is resynchronized with engine timing. Forexample, valve timing is aligned with the desired cycle of therespective cylinder. Further, the resynchronization may be attemptedafter a predetermined number of cylinder cycles.

If the valve does not follow the desired valve trajectory and the valvecurrent in each region is greater than cur_lim, the routine proceeds tostep 3918. If the valve current is less than cur_lim the routineproceeds to step 3920.

In step 3918, the number of valve restart attempts at a current level ofcur_lim, Rcl_dec, is compared to a predetermined variable, Rcl_deg_lim.If the number of restart attempts is greater than Rcl_deg_lim, theroutine proceeds to step 3930. If the number of restart attempts is lessthan Rcl_deg_lim the routine proceeds to step 3924. This decision logicallows the routine to make a predetermined number of valve restartattempts before deactivating the cylinder and valve.

In step 3924, a count representing the number of valve restart attemptsat the current amount in the cur_lim variable is incremented. Each timethe routine executes this logic the variable Rcl_deg is incremented.This variable allows the routine to deactivate the off-trajectory valveand the cylinder in which it resides to be deactivated if apredetermined number of attempts are exceeded, steps 3918 and 3930. Theroutine proceeds to exit after incrementing the variable.

In step 3920, valve restart attempts are compared to a predeterminedvalue. A variable, Rcl, representing the number of restart attempts at acurrent amount below cur_lim is compared to a predetermined value,Rcl_lim. If the number of restart attempts is greater than thepredetermined value the routine proceeds to step 3922. If the number ofrestart attempts is less than the predetermined value the routineproceeds to step 3926.

In step 3926, a count representing a number of valve restart attemptsbelow a current amount stored in Rcl_lim is incremented. Afterincrementing Rcl the routine proceeds to step 3928.

In step 3928, valve current is adjusted. The before-mentioned valvecontrol current vector, CL_cur_set, is adjusted by a predeterminedamount, Δ_adjust_up, each time a valve restart is attempted. Further, ifa valve is restarted below the nominal engine operating temperature,CL_adjust is not adjusted, but valve current compensation based ontemperature, Vt_adjust, is incremented by a predetermined amount at thetemperature where the valve restart attempt is made. The valve currentadjustment is adjusted by the equation:CL_cur_set=Vt_adjust·(CL_base_set+CL_adjust)Where CL_cur_set is current vector at the engine operating conditions,Vt_adjust is a function that is indexed by engine or valve temperature,CL_base_set is a vector containing base current amounts, and CL_adjustis a vector of adjustment current amounts at the engine operatingconditions. Following the current adjustment the routine exits.

In step 3922, valve current is set to a predetermined amount. Afterattempting to restart an off-trajectory valve a predetermined number oftimes, CL_cur_set is set to cur_lim. This may allow a valve to restartsooner than by continuing to make small incremental current increases.In addition, a variable vector, Alow, is loaded with the latest value ofCL_cur_set. By loading CL_adjust into Alow the routine adapts the valvecurrent based on engine operating conditions. The routine then proceedsto exit.

In step 3932, on-trajectory valve event counter is incremented. Thenumber of on-trajectory valve events, openings and closings, Vlv_cnt, isincremented when no trajectory error is detected. By accounting for thenumber of on-trajectory valve operations the method may reduce valvecurrent from the amount stored in cur_lim. The routine then proceeds tostep 3934.

In step 3934, valve current is compared to a predetermined amount. Ifthe valve current is greater than the amount stored in cur_lim theroutine proceeds to step 3936. If the valve current is less than theamount stored in cur_lim the routine exits.

In step 3936, the number of on-trajectory valve events, Vlv_cnt, iscompared to a predetermined amount, Vlv_on_traj. If Vlv_cnt is greaterthan Vlv_on_traj the routine proceeds to step 3938. If Vlv_cnt is lessthan Vlv_on_traj the routine exits.

In step 3938, valve current, CL_cur_set is adjusted to a lower amount.After a predetermined number of on-trajectory valve events the valvecurrent is lowered by a predetermined amount, Δ_adjust_dn. By loweringthe valve current after a predetermined number of on-trajectory eventsthe routine can quickly restart valves and then locate a current amountthat operates the valve while decreasing electrical losses and improvingfuel economy. Therefore, step 3938 provides a current adapting operationfor the routine. The routine then exits.

Referring to FIG. 40, a plot of valve trajectory regions during anopening and closing valve event is shown. In the method of FIG. 39,valve trajectories during opening and closing events are compared topredefined valve trajectories such as those shown in FIG. 40 todetermine valve error trajectories. The valve trajectory is separatedinto seven regions, regions 1-4 describe valve opening and regions 4-7describe valve closing. By comparing regions of the valve trajectory forvalve trajectory errors, the valve restart method can increase ordecrease valve current in specific regions. This allows the method ofFIG. 39 to adjust valve current in a desired region without increasingvalve current in other regions, thereby improving engine and electricalefficiency.

Valve current during valve opening and closing is also separated intoregions, similar to those shown in FIG. 40. Valve current in and aroundvalve trajectory error regions can be adjusted to reestablishon-trajectory valve operation. Furthermore, valve trajectories andcurrent amounts can be divided into a fewer or greater number of regionsthan shown in FIG. 40.

Referring to FIG. 41, a plot of an example valve current produced by themethod of FIG. 39 is shown. Once a valve trajectory error is indicated,valve current is adjusted slowly and then steps up to CL_lim. Further,after the valve is restarted, the valve current is reduced in thedirection of Alow.

Referring to FIG. 42, a flowchart of a method to improve individualcylinder air-fuel detection and control is shown. The method takesadvantage of the opportunity electromechanical valves present to improveindividual cylinder air-fuel detection and control by providingseparation, at least under some conditions, between individual cylinderexhaust pressure events.

Combustion in a cylinder produces pressures above atmospheric pressurethat act on a piston, moving the piston, and expanding the cylindervolume. Exhaust valves open to release cylinder pressure and exhaust thecombusted gas mixture. The pressure differential between the exhaustmanifold and the end of the tailpipe, which is at atmospheric pressure,causes exhaust to flow from a cylinder head to the tailpipe. The exhaustflow rate is a function of the exhausted cylinder pressure, the exhaustsystem volume, manifold and pipe geometry, and resistance of elements inthe exhaust passage. By increasing the number of crank angle degreesbetween cylinder combustion events, additional time is provided betweencombustion events. This allows higher-pressure exhaust gases at thecylinder head to migrate toward the tailpipe, equalizing exhaust systempressure. Since exhaust pressure is the mechanism that carries thecombusted exhaust gas information, e.g., air-fuel ratio, the additionalspace between combustion events reduces the amount of residual exhaustgas from previous combustion events at the oxygen sensor location, FIG.1, 76.

The inventors herein have discovered that electromechanical valves mayimprove individual cylinder air-fuel separation and control.Electromechanical valves can extend the distance between cylinder ventsby altering exhaust valve timing, operating in a multi-stroke cylindermode while providing the desired amount of engine torque. Also note thatin one example, multi-stroke operation can be combined along withvarying the number of active valves in the cylinders (or by varying thenumber of active valves between different cylinder groups operating inmulti-stroke), and with deactivating cylinders. Such operation can alsoimprove torque control by enabling finer torque resolution in differentmodes.

The method of FIG. 42 may be integrated into the cylinder and valve modeselection routine, FIG. 10 or alternately, as shown here, as astand-alone function that repeatedly executes until all cylinders areadjusted at a given engine speed and load.

In step 4210, operating conditions are determined. For example, theroutine evaluates rates of change in engine speed and desired torque todetermine if individual cylinder air-fuel detection and control shouldbe permitted. If high rates of change in engine speed or desired torqueoccur, the routine is exited because individual cylinder air-fueldetection can become more difficult. In addition, engine temperature andvalve operating conditions can further restrict entry into the routing.If stabilized operating conditions are present, the routine proceeds tostep 4212, if not, the routine proceeds to exit.

In step 4212, cylinder and valve modes to improve individual cylinderair-fuel detection are selected. Based on the desired engine torque,cylinder and valve modes are selected to improve individual cylinderair-fuel detection. The method can choose to modify exhaust valvetiming, enter multi-stroke cylinder operation, or deactivate selectedcylinders or combinations or sub-combinations thereof. If selectedcylinders are deactivated for a period, deactivated cylinders are laterreactivated and other cylinders are deactivated. This allows allcylinders to be individually adjusted, if desired, as the routineexecutes.

Alternatively, the cylinder and valve mode may be selected by the methodof FIG. 10. If a selected cylinder and valve mode is appropriate forindividual cylinder air fuel detection, the routine is executed.

In step 4214, cylinder and/or valve mode are set. As discussed above,the routine selects cylinder and/or valve modes from a group ofavailable modes that can increase the separation between cylinderevents. This can be accomplished by selecting from the above-mentionedcylinder and valve modes or additionally by grouping combinations ofcylinder and valve modes. For example, a 4-cylinder engine may beoperated with 2 cylinders in four-stroke mode and 2 cylinders insix-stroke mode. Further, the spark timing, air-fuel ratio, and aircharge amounts can be increased or decreased between cylinder groups.These variables allow increased signal to noise ratios in the cylindersbeing evaluated. For example, air-fuel ratio can be made rich or lean inone group of cylinders and stoichiometric in another group. Alternately,one group compared to another may induct an additional air amount thatwill increase cylinder pressure. Further, spark adjustments may be madebetween cylinders groups to balance torque generation between thegroups.

In addition, grouping valves in different ways enables cylinder specificdiagnostics to be performed. For example, all cylinders, with theexception of the cylinder being evaluated, can be operated in a baseconfiguration. The cylinder under evaluation, e.g., the second cylindergroup, is operated with additional valves to provide additional flow andpotentially a different air-fuel ratio. By operating in thisconfiguration, assessment of the operation of a specific cylinder can beless perceptible than by other methods.

Also, different valve patterns in different cylinder groups may alsoprovide an advantage of different cylinders to producing differentcombustion products at similar torque levels. This permits engineemissions to be adapted to a specific catalyst system. As mentionedabove, asymmetric exhaust systems with different catalyst locationsbetween engine bank is one example. Further, different shape catalystsand different catalyst substrate densities can also be compensated. Theselected valve and cylinder configuration is activated, then the routineproceeds to step 4216.

In step 4216, individual cylinder air-fuel ratios are determined. Afterthe individual cylinder events have been separated, by altered valvetiming and/or configurations, a predetermined time is allowed to expirethat allows the system to reach an equilibrium condition. Then oxygensensor sampling is adjusted to correspond to the altered cylinderoperation and pressure signal. The sampling is adjusted so that a sampleis taken after the peak pressure passes the oxygen sensor. This allowsthe cylinder pressure of the latest combustion event to push a largerfraction of past combustion event gases out the tail pipe before asample is taken.

Next, the method employs the method of U.S. Pat. No. 5,515,828, which ishereby fully incorporated by reference, to determine individual cylinderair-fuel ratio adjustments. These adjustment amounts may be stored inmemory to produce continually adaptive cylinder adjustments. Onceindividual cylinder adjustment amounts are determined, the routineproceeds to step 4218.

In step 4218, engine air or fuel adjustments are made. Becauseelectromechanical valve timing may be adjusted with little restriction,valve timing adjustments may be made to compensate for air-fuel errors.This is accomplished by allowing a small offset between the desiredvalve timing and the final valve timing. For example, IVC valve timingfrom FIG. 2, step 226, may be altered by adding an offset to thedetermined IVC timing, e.g., IVC_final=IVC+ΔIVC. The valve timingadjustment is limited to restrict changes in engine torque production.

Alternatively, the amount of fuel delivered to individual cylinders mayalso be adjusted. Fuel adjustments are made to balance air-fuel in step220 of FIG. 2. An offset alters the desired lambda value, e.g.,LAM_Fin=LAMBDA+ΔLAM. However, step 222 continues to use the base LAMBDAvalue to determine the desired air charge. This allows fuel changeswithout significantly affecting air charge and torque production. Fuelamount adjustments are also limited to ensure system robustness. Theroutine then exits.

Referring to FIG. 43, a plot of simulated normalized exhaust mass, whichis a function of engine crankshaft angle, from a few of the previouslymentioned cylinder and valve modes used to improve air-fuel detection isshown.

The first plot shows normalized exhaust mass in a four-cylinder engineoperating in four-stroke cylinder mode. The mass traces are generallysymmetric, whereas an actual engine may produce slight phase differencesat the confluence point because of transmission distance differences inthe exhaust system that result from cylinder and sensor location. Also,the signal peaks, indicative of exhausted combustion events, occur atshorter intervals compared to the other plots.

The second plot shows a four-cylinder engine operating with four activecylinders in four-stroke mode and with two of the four cylinders withdelayed exhaust valve timing. Cylinders with delayed exhaust valvetiming combust every other combustion event. This mode provides lesssignal separation than the modes of the third plot, but all fourcylinders are active, providing additional torque capacity. Late exhaustvalve opening can increase the crank angle duration between combustionin cylinders with nominal exhaust valve timing and cylinders withretarded exhaust valve timing. However, since four-cylinders combust atthe same rate as the first plot, the crank angle duration betweencylinders with delayed exhaust valve timing and cylinders having nominalexhaust valve timing decreases. Further, delaying exhaust valve timingcan improve cylinder air-fuel mixture identification in cylinders withnominal exhaust valve timing because it can provide additional time forexhaust from previous combustion events to be expelled to theatmosphere. Consequently, the exhaust gas sample may be closer to theactual cylinder air-fuel mixture.

The third plot shows a four-cylinder engine operating with 2 activecylinders. Comparing the first plot to the third plot illustrates theseparation in the mass peaks. This signal separation can be used toadvantage to enable better determination of individual cylinder air-fuelratios. Again, the separation between cylinder events may add additionaltime for the exhaust from previous combustion events to be expelled tothe atmosphere.

FIGS. 44-48 show various alternative embodiment valve/cylinderconfigurations which can be used with the above described system andmethods.

Referring now specifically to FIG. 44, a plot shows intake and exhaustevents in a cylinder operating in four-stroke cylinder mode, with fourvalves per cylinder, and the valves operating in a alternatingintake/dual exhaust configuration. Valve timing is referenced totop-dead-center of combustion being zero degrees.

The top two traces show intake valves opening in an alternating pattern,every other combustion event. That is, intake valve “A” opens every 1440crank angle degrees, and intake valve “B” opens every 1440 crank angledegrees. Valve “A” and valve “B” opening events are separated by 720degrees. Alternatively, a phase angle between intake valve “A” andintake valve “B” may also be added.

The bottom two traces show both exhaust valves opening every 720degrees. Alternatively, a phase angle difference may be added betweenexhaust valve events, but in this example both exhaust valves open aftera combustion event.

This valve operating configuration may be selected by the mode controlmatrix to reduce electrical power consumption and to change airinduction characteristics. In addition, this valve configuration may beused in other multi-stroke cylinder modes and/or in an engine with atleast some deactivated cylinders.

Referring to FIG. 45, a plot shows intake and exhaust events in acylinder operating in four-stroke cylinder mode, with four valves percylinder, and the valves operating in a alternating intake/alternatingexhaust configuration. Valve timing is referenced to top-dead-center ofcombustion being zero degrees.

The top two traces show intake valves opening in an alternating pattern,every other combustion event. That is, intake valve “A” opens every 1440crank angle degrees, and intake valve “B” opens every 1440 crank angledegrees. Valve “A” and valve “B” opening events are separated by 720degrees. Alternatively, a phase angle between intake valve “A” andintake valve “B” may also be added.

The bottom two traces show exhaust valves opening in an alternatingpattern, every other combustion event. That is, exhaust valve “A” opensevery 1440 crank angle degrees, and exhaust valve “B” opens every 1440crank angle degrees, valve “A” and valve “B” opening events areseparated by 720 degrees. Alternatively, a phase angle between exhaustvalve “A” and exhaust valve “B” may also be added.

This valve operating configuration may also be selected by the modecontrol matrix to reduce electrical power consumption and to change airinduction characteristics. Furthermore, operating valves in analternating configuration may reduce valve degradation. In addition,this valve configuration may be used in other multi-stroke cylindermodes and/or in an engine with at least some deactivated cylinders.

Referring to FIG. 46, a plot shows intake and exhaust events in acylinder operating in four-stroke cylinder mode, with four valves percylinder, and the valves operating in a single intake/alternatingexhaust configuration. Valve timing is referenced to top-dead-center ofcombustion being zero degrees.

The top two traces show intake valve “A” opening before each combustionevent. Intake valve “B” is deactivated in a closed position.Alternatively, intake valve “B” may be operated while intake valve “A”is deactivated in a closed position.

The bottom two traces show exhaust valves opening in an alternatingpattern, every other combustion event. That is, exhaust valve “A” opensevery 1440 crank angle degrees, and exhaust valve “B” opens every 1440crank angle degrees. Valve “A” and valve “B” opening events areseparated by 720 degrees. Alternatively, a phase angle between exhaustvalve “A” and exhaust valve “B” may also be added.

This valve operating configuration may also be selected by the modecontrol matrix to reduce electrical power consumption and to change airinduction characteristics.

Referring to FIG. 47, a plot shows intake and exhaust events in acylinder operating in four-stroke cylinder mode, with four valves percylinder, and the valves operating in a alternating intake/singleexhaust configuration. Valve timing is referenced to top-dead-center ofcombustion being zero degrees.

The top two traces show intake valves opening in an alternating pattern,every other combustion event. That is, intake valve “A” opens every 1440crank angle degrees, and intake valve “B” opens every 1440 crank angledegrees, valve “A” and valve “B” opening events are separated by 720degrees. Alternatively, a phase angle between intake valve “A” andintake valve “B” may also be added.

The bottom two traces show exhaust valve “A” opening after eachcombustion event. Exhaust valve “B” is deactivated in a closed position.Alternatively, exhaust valve “B” may be operated while exhaust valve “A”is deactivated in a closed position.

This valve operating configuration may also be selected by the modecontrol matrix to reduce electrical power consumption and to changeexhaust flow characteristics.

Referring to FIG. 48, a plot shows intake and exhaust events in acylinder operating in four-stroke cylinder mode, with four valves percylinder, and the valves operating in a dual intake/alternating exhaustconfiguration. Valve timing is referenced to top-dead-center ofcombustion being zero degrees.

The top two traces show both intake valves opening every 720 degrees.Alternatively, a phase angle difference may be added between intakevalve events, but in this example both intake valves open before acombustion event. Alternatively, a phase angle between intake valve “A”and intake valve “B” may also be added.

The bottom two traces show exhaust valves opening in an alternatingpattern, every other combustion event. That is, exhaust valve “A” opensevery 1440 crank angle degrees, and exhaust valve “B” opens every 1440crank angle degrees. Valve “A” and valve “B” opening events areseparated by 720 degrees. Alternatively, a phase angle between exhaustvalve “A” and exhaust valve “B” may also be added.

This valve operating configuration may also be selected by the modecontrol matrix to reduce electrical power consumption, increaseperformance, and to change exhaust flow characteristics.

As described above with regard to FIGS. 33 a and 33 b, electromechanicalvalves may be used to improve engine starting and reduce engineemissions. FIGS. 49 through 54 present alternative valve sequences thatmay be used in engines with electromechanical valves or with valves thatmay be mechanically deactivated. The figures show four-cylinderoperation for simplicity, but the methods can be carried over to engineswith fewer or additional cylinders.

As described above and below, any of the above operating modes can beused alone or in combination with one another, and/or in combinationwith varying the number of strokes of the cylinder cycle, phased intake,and/or phased exhaust valve opening and/or closing.

Referring to FIGS. 49 a and 49 b, the plots show intake and exhaustvalve timing during a start for an engine with mechanical exhaust valvesand valves that may be held in an open position, electromechanicalvalves for example.

The intake valves are set to an open position after a key on isobserved. As the starter rotates the engine, the mechanically drivenexhaust valves open and close based on the engine position and camtiming. At the vertical sync line, a point shown for illustration andthat may vary depending on system configuration, the engine controller12 determines engine position from crankshaft sensor 118. A delay timeis shown between sync and the first valve operation (opening/closing),the actual delay may be shorter or longer. After engine position isknown, the intake valves are held open until before fuel is injectedinto an intake port of a cylinder selected for a first combustion event.Alternatively, the intake valve may be held open and fuel injectedduring a first intake stroke.

By holding the intake valves in an open position, residual hydrocarbonspumped through the engine as the engine rotates can be reduced.

Opening intake and exhaust valves during the same crank angle intervalallows a portion of residual hydrocarbons to be pumped into the intakemanifold where the hydrocarbons can be inducted and combusted after afirst combustion event.

As described above, the individual cylinder intake valves are held openuntil before fuel is injected into the ports of respective cylinders.After the valve is closed, fuel is injected, and then induction andfour-stroke valve sequence begins. Alternatively, cylinders can beoperated in multi-stroke modes and/or fuel may be injected on an openvalve. Furthermore, fuel may be injected after the induction stroke ondirect injection engines.

Referring to FIGS. 50 a and 50 b, the plots show intake and exhaustvalve timing during a start for an engine with valves that may beoperated before combustion in a selected cylinder occurs,electromechanical valves for example.

The intake valves are set to an open position after a key on isobserved. As the starter rotates the engine, the mechanically drivenexhaust valves open and close based on the engine position and camtiming. At the vertical sync line, a point shown for illustration andthat may vary depending on system configuration, the engine controller12 determines engine position from crankshaft sensor 118. After engineposition is known, the intake valves are closed when the exhaust valvesare open, and the intake valves are held open when the exhaust valvesare closed, until before fuel is injected into a intake port of acylinder selected for a first combustion event.

By following this sequence, engine pumping work can be reduced, butthere may be some net residual hydrocarbon flow through the engine.

As described above, the intake valves are closed when the exhaust valvesare open, and the intake valves are held open when the exhaust valvesare closed. Fuel is injected on a closed intake valve prior to aninduction event in respective cylinders. Alternatively, cylinders can beoperated in multi-stroke modes and/or fuel may be injected on an openvalve. Furthermore, fuel may be injected after the induction stroke ondirect injection engines.

Referring to FIGS. 51 a and 51 b, the plots show intake and exhaustvalve timing during a start for an engine with valves that may beoperated before combustion in a selected cylinder occurs,electromechanical valves for example.

The intake valves are set to an open position after a key on isobserved. As the starter rotates the engine the mechanically drivenexhaust valves open and close based on the engine position and camtiming. At the vertical sync line, a point shown for illustration andthat may vary depending on system configuration, the engine controller12 determines engine position from crankshaft sensor 118. After engineposition is known, the intake valves are open during crank angleintervals that can be intake and compression strokes of four-strokecylinder operation. During crank angle intervals that can be consideredpower and exhaust strokes of four-stroke cylinder operation, the intakevalves are closed. This sequence occurs until before fuel is injectedinto the intake port of a cylinder selected for a first combustionevent.

By following this sequence, engine pumping work may be increased, butnet residual hydrocarbon flow through the engine can be reduced. And, insome cases, net flow through the engine is reversed, such that gassesfrom the exhaust manifold are pumped into the intake manifold, beforefuel injection is commenced.

Fuel is injected on a closed intake valve prior to an induction event inrespective cylinders. Alternatively, cylinders can be operated inmulti-stroke modes and/or fuel may be injected on an open valve.Furthermore, fuel may be injected after the induction stroke on directinjection engines.

Referring to FIGS. 52 a and 52 b, the plots show intake and exhaustvalve timing during a start for an engine with valves that may be heldin a position, electromechanical valves for example.

The intake valves are set to an open position and the exhaust valves areset to a closed position after a key on is observed. At the verticalsync line, a point shown for illustration and that may vary depending onsystem configuration, the engine controller 12 determines engineposition from crankshaft sensor 118. A delay time is shown between syncand the first valve operation (opening/closing), the actual delay may beshorter or longer. After engine position is known, the intake valves areheld open until before fuel is injected into the intake port of acylinder selected for a first combustion event.

By holding the intake valves in an open position and exhaust valves in aclosed position, engine pumping work and residual hydrocarbons pumpedthrough the engine as the engine rotates can be reduced. Opening intakevalves can reduce engine pumping work since air can pass in and out of acylinder as a piston travels toward or away from the cylinder head.Holding residual hydrocarbons in an engine and combusting thehydrocarbons may reduce the amount of hydrocarbons emitted into theexhaust since residual hydrocarbons may be converted into otherconstituents, namely CO₂ and H₂O, during combustion.

Referring to FIGS. 53 a and 53 b, the plots show intake and exhaustvalve timing during a start for an engine with valves that may be heldin a position, electromechanical valves for example.

The intake valves are set to a closed position and the exhaust valvesare set to an open position after a key on is observed. At the verticalsync line, a point shown for illustration and that may vary depending onsystem configuration, the engine controller 12 determines engineposition from crankshaft sensor 118. A delay time is shown between syncand the first valve operation (opening/closing), the actual delay may beshorter or longer. After engine position is known, the intake valve isheld closed until fuel is injected into the intake port of therespective cylinder, and then the intake valve opens to induct anair-fuel mixture.

The exhaust valves are held in an open position until before a firstinduction event in the respective cylinder. After the exhaust valves areclosed, exhaust valve operation is based on the operational stroke ofthe cylinder, four-stroke for example.

By holding the intake valves in a closed position and exhaust valves inan open position, engine pumping work and residual hydrocarbons pumpedthrough the engine as the engine rotates can be reduced. Opening exhaustvalves can reduce engine pumping work since air can pass in and out of acylinder as a piston travels toward or away from the cylinder head.However, the net air flow through the engine remains low since theintake valves are held in a closed position.

Since engines having electromechanical valves are not mechanicallyconstrained to operate at fixed crankshaft positions, valve timing maybe set to produce a desired stroke in a selected cylinder. For example,a piston that is traveling toward the cylinder head may be set to acompression or exhaust stroke by adjusting valve timing. In one example,setting the stroke of a cylinder can be described by FIG. 54.

Referring to FIG. 54 a plot shows piston trajectories for two pistons ina four-cylinder engine over two engine revolutions. The pistontrajectory of the top plot and the piston trajectory of the bottom plotare 180 crank angle degrees out of phase. That is, one piston is at thetop of the cylinder while the other piston is at the bottom of acylinder.

Three symbols (o, *, and Δ) identify example engine positions where anengine controller may determine engine position during a start. Inaddition, four vertical lines pass through both plots to illustratemoveable decision boundaries where cylinder strokes can be determined.The number of decision boundaries can vary with the number of cylindersin an engine. Typically, one decision boundary is selected for every twocylinders in an engine.

Setting the stroke (e.g., intake, combustion, compression, or exhaust)for a cylinder capable of a first combustion event may be accomplishedbased on a number of engine operating conditions, control objectives,and may include a decision boundary. For example, after engine positioncan be established, a decision boundary can be used as a location, overa crank angle interval, to set a stroke of a particular cylinder, basedon engine operating conditions and control objectives. A four-cylinderengine with control objectives of a first combustion event in cylindernumber one, producing a desired torque resulting from combustion eventnumber one, could set the stroke of cylinder one, providing criteria aremet, at or before a decision boundary. The remaining cylinder strokescan be set based on a predetermined order of combustion.

The decision boundary can be described as a location in crankshaftdegrees relative to a piston position. In FIG. 54, the decision boundary1 is at approximately 170 degrees after top-dead-center of cylinder “B”.Decision boundary 2 is at approximately 350 degrees aftertop-dead-center of cylinder “B”.

As the engine rotates, based on the determined engine operatingconditions, cylinder stroke for respective cylinders may be set byadjusting valve timing, before and up to, a boundary condition. Twoboundary conditions, decision boundary 1 and decision boundary 2, areshown in FIG. 54 because the illustrated cylinder trajectories are outof phase and the second boundary condition may be encountered,permitting setting of cylinder stroke, before the piston locationrepresented by decision boundary 1 is reencountered. In other words, inthis example, decision boundary 1 and 2 represent the same cylinderstroke setting opportunity, albeit in different cylinders.

Of course, the boundary conditions can move based on engine operatingconditions and control objectives. For example, boundary conditions maybe moved, relative to crankshaft angle, based on engine temperature orbarometric pressure. When a decision boundary is encountered, engineoperating parameters are evaluated to determine if the stroke of enginecylinders can be set. For example, if engine position and engine speedand/or acceleration permits induction of a desired air amount that canproduce a desired engine output, a selected cylinder may be set to aninduction stroke. Specifically, desired engine outputs can includedesired engine torque, a desired cylinder air amount, and a desiredengine speed. However, if operating conditions do not permit setting thestroke of a cylinder at the present boundary, then the next boundarycondition factors into setting the cylinder stroke.

Referring again to FIG. 54, the “o” signifies a location where engineposition might be established. If engine operating conditions meetcriteria for setting the stroke of a cylinder before decision boundary 1is encountered, the stroke of a selected cylinder can be set. In oneexample, cylinder “B” may be set to an intake stroke by adjusting valvetiming such that cylinder “B” is the first cylinder to combust. Theremaining cylinders are set to strokes based on a firing order, 1-3-4-2in a four cylinder engine for example. In other words, if cylindernumber one is set to an intake stroke, cylinder number three is set toan exhaust stroke, cylinder number four is set to a power stroke, andcylinder number two is set to a compression stroke. However, asdescribed above, selected valve events may not follow four-strokecylinder timings, up to a first combustion event, so that enginestarting can be improved. On the other hand, if after evaluation engineoperating conditions, the cylinder stroke cannot be set, the next strokesetting opportunity is at decision boundary 2.

The “*” signifies another engine position where engine position might beestablished. Again, if engine operating conditions meet criteria forsetting the stroke of a cylinder before decision boundary 1 isencountered, the stroke of the selected cylinder is set. However, the“*” position occurs closer to decision boundary than the “o” position.When engine position is determined closer to the decision boundary,opportunity to set the stroke of a cylinder can decrease. For example,if an engine is beginning to rotate and engine position is establishednear a decision boundary, there may not be a sufficient duration orsufficient upward or downward movement to induct a desired cylinder airamount and produce an engine output. In this example, setting thecylinder stroke may be delayed until the next decision boundary underthese conditions.

The “Δ” signifies yet another engine position where engine positionmight be established. In this position, if engine operating conditionsmeet criteria for setting the stroke of a cylinder before decisionboundary 2 is encountered, the stroke of the selected cylinder is set.Specifically, in this case, cylinder “A” is set to an intake stroke andfueled to be the first cylinder to carry out combustion. Decisionboundary 1 and 2 can be used to set the stroke of different cylindersthat produce a first combustion event.

As described above, various valve sequences can be used to vary valvetiming (of electromechanical valves, for example) to be different before(and/or during) a first combustion event (or a first fuel injectionevent), compared with valve timing after a first combustion event. Eachof the above embodiments offer different advantages that can be used toimprove engine operation.

Referring to FIG. 55, a flowchart shows a method to adjust air-fuelbased on a selected cylinder and/or valve mode.

As described above, cylinder and valve modes may be used to improveperformance and fuel economy. However, without controlling the state ofa catalyst (amount of stored oxidants, temperature, etc.) duringcylinder and/or valve mode changes, and while in the different cylinderand/or valve modes, emissions may increase. Fuel and spark are twocontrol parameters that can be used to adjust the state of a catalyst.The method of FIG. 55 works in conjunction with the method of FIG. 10 toaffect the catalyst state by adjusting fuel delivered to the engine.

In step 5510, the routine determines if a mode change has been requestedby step 1022 of FIG. 10. A mode change request is indicated by adifference between the requested mode variable and the target modevariable. If a mode change is not pending, the routine proceeds to step5520. If a mode change is pending, the routine proceeds to step 5512.

In step 5512, the routine determines if the requested engine torque isincreasing. If so, the routing proceeds to step 5522. If not, theroutine proceeds to step 5514. This step allows a cylinder and/or valvemode change to occur without a long delay if the driver is requestingadditional torque, which can improve vehicle drivability.

In step 5514, the routine delays an impending cylinder and/or valve modechange. The routine sends a signal, by setting the MODE_DLY variable, tostep 1022 of FIG. 10. The duration of the delay may be based on timeand/or on the oxidant state and/or oxidant storage capacity of thecatalyst. For example, the oxidant storage capacity of a catalyst andthe amount of oxidants stored in the catalyst may be sufficient to allowa mode change by the method of FIG. 14, but this routine may delay themode change to further adjust the catalyst state by increasing ordecreasing fuel to the engine. Typically, the delay is maintained untilthe oxidant storage capacity reaches a predetermined level that is basedon the new cylinder and/or valve mode. The routine then continues tostep 5516.

In step 5516, the routine determines if the delay is complete. If thedelay is complete the routine continues to step 5524. If the delay isnot complete the routine proceeds to step 5518.

In step 5518, the fuel delivered to the engine is adjusted. The fueladjustment amount is based on the new cylinder and/or valve mode, engineoperating conditions, and catalyst conditions. For example, if theengine was operating in a fuel enrichment mode to regulate catalysttemperature, the fuel amount may be leaned to return the catalyst from ahydrocarbon rich state. On the other hand, if the engine has beenoperating with eight cylinders at low or moderate loads, and a reducedcylinder mode is requested, the fuel amount may be enriched toanticipate higher levels of NO_(x) that may occur in reduced cylindermodes. Fuel is adjusted by increasing or decreasing the average amountof fuel delivered to the engine, by biasing the fuel for example.Alternatively, fuel amounts may be pulsed or stepped to increase ordecrease the amount of oxidants stored in the catalyst. The effect ofthis step can be to pre-condition the state of the catalyst for theimpending cylinder and/or valve mode change. Then, the routine exits.

In step 5524, the routine enables a requested cylinder and/or valvemode. After the predetermined delay is been met, the MODE_DLY variableis set to an off state, permitting the mode change in step 1022 of FIG.10. The routine proceeds to exit after turning off the mode delay flag.

In step 5522, fuel delivered to the engine is adjusted based on the newcylinder and/or valve mode. This path of the routine does not delay animpending cylinder and/or valve mode request, but the fuel may beenriched or leaned during the period between setting the requested modevariable and setting the target mode variable. This feature may also beused to pre-condition the catalyst before an impending cylinder and/orvalve mode change. The routine proceeds to exit.

In step 5520, fuel is adjusted based on the current cylinder and/orvalve mode. Switching cylinder and/or valve modes may alter engine feedgas constituents. It may be beneficial to adjust the amount of fueldelivered to the engine to compensate for exhaust gases produced byspecific cylinder and/or valve modes. Therefore, the base fuel deliveredto the engine can be adjusted to provide the before-mentionedcompensation. For example, the desired base fuel amount may produce astoichiometric air-fuel mixture, such as approximately 14.6 for example.Fuel compensation can be determined by looking up a fuel bias amountfrom a matrix of fuel bias amounts, MODE_BIAS. In this example, anenrichment request of 0.2 air-fuel ratios may be requested. The fuelbias can then reduce the air-fuel mixture to produce a 14.4 air-fuelratio mixture. Compensation for each cylinder and/or valve mode isprovided. The routine proceeds to exit.

As will be appreciated by one of ordinary skill in the art, the routinesdescribed in FIGS. 2, 10, 13-18, 32, 37 and 39 may represent one or moreof any number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various steps or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages described herein, but are provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

It will be appreciated that the various operating modes described aboveare exemplary in nature, and that these specific embodiments are not tobe considered in a limiting sense, because numerous variations arepossible. The subject matter of the present disclosure includes allnovel and non-obvious combinations and subcombinations of the valveoperating patters, cylinder operating patterns, cylinder strokevariations, valve timing variations, and other features, functions,and/or properties disclosed herein.

For example, in one example, an approach can be used where the enginevaries the number of cylinders carrying out combustion. Further, notonly can the number of the cylinders carrying out combustion be varied,but the number of valves in active cylinders can also be varied (intime, or between different cylinder groups). Further still, in additionor as an alternative, the number of stroke in active cylinders can bevaried (in time, or between different cylinder groups). Thus, in oneexample, in a first mode the engine can operate with a first number ofcylinders carrying out combustion with a first number of strokes and afirst number of active valves, and in a second mode, the engine canoperate with a second number of cylinders carrying out combustion with asecond number of strokes and a second number of active valves. In thisway, greater torque resolution can be obtained with increasing fueleconomy. In another example, a first group of cylinders of the enginecan operate with a first number of strokes and a first number of activevalves, and a second group of cylinders of the engine can operate with asecond number of strokes and a second number of active valves. In stillanother example, the cylinders can have equal number of valves active,yet different valve patterns (e.g., one group of cylinder can have theactive intake valve and exhaust valve in a diagonal configuration, whileanother group has a non-diagonal configuration).

Further, in one approach, the control system can use a combination ofvarying the number of cylinders carrying out combustion, varying thenumber (or pattern) of active valves, and/or varying the number ofstrokes of active cylinders as ways to control engine output torque. Byhaving numerous degrees of freedom, it can be possible to betteroptimize engine performance for various operating conditions.

Also, in one example described above, the number of strokes can bevaried as a condition of a catalyst in the exhaust system varies, suchas, for example, the amount of stored oxidants. However, other engineparameters can also be adjusted based on catalyst conditions, such asthe number of active valves in active cylinders, and/or the pattern ofactive valve in active cylinders. Further, the number of cylinderscarrying out combustion can also be varied as catalyst conditions vary.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the valve operating patters,cylinder operating patterns, cylinder stroke variations, valve timingvariations, and/or properties may be claimed through amendment of thepresent claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the disclosure. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in diesel, naturalgas, gasoline, or alternative fuel configurations could be used toadvantage.

1-25. (canceled)
 26. A system, comprising: a hybrid-electric vehicle; anengine coupled in the hybrid-electric vehicle, the engine having atleast a cylinder with an electrically actuated valve; a controllerconfigured to: deactivate the cylinder by deactivating the electricallyactuated valve of the cylinder; vary a number of strokes in a combustioncycle of the cylinder via the electrically actuated valve of thecylinder; and vary a valve pattern of the cylinder; wherein thevariation between includes a region of operating valves in the cylinderbetween a first pattern during a first condition and a second patternduring a second condition.
 27. The system of claim 26 wherein theconditions include temperature.
 28. The system of claim 26 wherein theconditions include engine speed.
 29. The system of claim 26 wherein theconditions include a condition of the electrically actuated valve. 30.The system of claim 26 wherein the conditions include a temperature ofan actuated coupled to the electrically actuated valve.
 31. The systemof claim 30 wherein said valve actuator is comprised of at least anarmature, a coil, and a core.
 32. The system of 31 wherein electricallyactuated valve is an intake valve
 33. A system, comprising ahybrid-electric vehicle; an engine coupled in the hybrid-electricvehicle, the engine having at least a first and second cylinder, eachwith an electrically actuated valve; a controller configured to:deactivate at least one of the cylinders by deactivating its respectiveelectrically actuated valve; vary a number of strokes in a combustioncycle of at least one of the cylinders via its respective electricallyactuated valve; and vary a valve pattern between the cylinders; whereinthe variation between valve patterns includes a region of operatingvalves in the cylinders.
 34. The system of 33 wherein the cylindersoperate with varied valve patterns during a common engine cycle.